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Groups > linux.kernel > #1487427 > unrolled thread

[PATCH 0/2 v2] cpu hotplug: Preserve topology directory after soft remove event

Started byPrarit Bhargava <prarit@redhat.com>
First post2016-09-20 17:30 +0200
Last post2016-09-20 17:30 +0200
Articles 4 — 2 participants

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Contents

  [PATCH 0/2 v2] cpu hotplug: Preserve topology directory after soft remove event Prarit Bhargava <prarit@redhat.com> - 2016-09-20 17:30 +0200
    [PATCH 1/2 v2] drivers/base: Combine topology.c and cpu.c Prarit Bhargava <prarit@redhat.com> - 2016-09-20 17:30 +0200
      Re: [PATCH 1/2 v2] drivers/base: Combine topology.c and cpu.c kbuild test robot <lkp@intel.com> - 2016-09-20 19:50 +0200
    [PATCH 2/2 v2] cpu hotplug: add CONFIG_PERMANENT_CPU_TOPOLOGY Prarit Bhargava <prarit@redhat.com> - 2016-09-20 17:30 +0200

#1487427 — [PATCH 0/2 v2] cpu hotplug: Preserve topology directory after soft remove event

FromPrarit Bhargava <prarit@redhat.com>
Date2016-09-20 17:30 +0200
Subject[PATCH 0/2 v2] cpu hotplug: Preserve topology directory after soft remove event
Message-ID<sjv9D-4MD-1@gated-at.bofh.it>
The information in /sys/devices/system/cpu/cpuX/topology
directory is useful for userspace monitoring applications and in-tree
utilities like cpupower & turbostat.

When down'ing a CPU the /sys/devices/system/cpu/cpuX/topology directory is
removed during the CPU_DEAD hotplug callback in the kernel.  The problem
with this model is that the CPU has not been physically removed and the
data in the topology directory is still valid.  IOW, the cpu is still
present but the kernel has removed the topology directory making it
very difficult to determine exactly where the cpu is located.

This patchset adds CONFIG_PERMANENT_CPU_TOPOLOGY, and is Y by default for
x86, an N for all other arches.  When enabled the kernel is modified so
that the topology directory is added to the core cpu sysfs files so that
the topology directory exists for the lifetime of the CPU.  When
disabled, the behavior of the current kernel is maintained (that is, the
topology directory is removed on a down and added on an up).  Adding
CONFIG_PERMANENT_CPU_TOPOLOGY may require additional architecture so that
the cpumask data the CPU's topology is not cleared during a CPU down.

This patchset combines drivers/base/topology.c and drivers/base/cpu.c to
implement CONFIG_PERMANENT_CPU_TOPOLOGY and leaves all arches except
x86 with the current behavior.

peterz asked when the topology directory is destroyed when
CONFIG_PERMANENT_CPU_TOPOLOGY=y.  The topology directory's lifetime will
change when CONFIG_PERMANENT_CPU_TOPOLOGY=y from existing when the thread
is online, to being created when the struct device associated with the thread
is created, and similarly being destroyed when the struct device is destroyed.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Len Brown <len.brown@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Juergen Gross <jgross@suse.com>

Prarit Bhargava (2):
  drivers/base: Combine topology.c and cpu.c
  cpu hotplug, add CONFIG_PERMANENT_CPU_TOPOLOGY

 arch/x86/kernel/smpboot.c |    3 -
 drivers/base/Kconfig      |   12 ++++
 drivers/base/Makefile     |    2 +-
 drivers/base/cpu.c        |  147 +++++++++++++++++++++++++++++++++++++++
 drivers/base/topology.c   |  168 ---------------------------------------------
 5 files changed, 160 insertions(+), 172 deletions(-)
 delete mode 100644 drivers/base/topology.c

-- 
1.7.9.3

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#1487432 — [PATCH 1/2 v2] drivers/base: Combine topology.c and cpu.c

FromPrarit Bhargava <prarit@redhat.com>
Date2016-09-20 17:30 +0200
Subject[PATCH 1/2 v2] drivers/base: Combine topology.c and cpu.c
Message-ID<sjv9D-4MD-7@gated-at.bofh.it>
In reply to#1487427
The topology.c file contains sysfs files that describe a cpu's location
and its siblings.  There is no purpose that this file is separate from
the core cpu code.  This patch combines topology.c into cpu.c to make the
next set of changes easier to understand.

There are no functional changes with this patch.

[v2]: fix error from ktest build robot with CONFIG_KEXEC=n

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Len Brown <len.brown@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
---
 drivers/base/Makefile   |    2 +-
 drivers/base/cpu.c      |  139 +++++++++++++++++++++++++++++++++++++++
 drivers/base/topology.c |  168 -----------------------------------------------
 3 files changed, 140 insertions(+), 169 deletions(-)
 delete mode 100644 drivers/base/topology.c

diff --git a/drivers/base/Makefile b/drivers/base/Makefile
index 2609ba20b396..e50491bb3d60 100644
--- a/drivers/base/Makefile
+++ b/drivers/base/Makefile
@@ -4,7 +4,7 @@ obj-y			:= component.o core.o bus.o dd.o syscore.o \
 			   driver.o class.o platform.o \
 			   cpu.o firmware.o init.o map.o devres.o \
 			   attribute_container.o transport_class.o \
-			   topology.o container.o property.o cacheinfo.o
+			   container.o property.o cacheinfo.o
 obj-$(CONFIG_DEVTMPFS)	+= devtmpfs.o
 obj-$(CONFIG_DMA_CMA) += dma-contiguous.o
 obj-y			+= power/
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 691eeea2f19a..c59cecbb651a 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -180,6 +180,145 @@ static struct attribute_group crash_note_cpu_attr_group = {
 };
 #endif
 
+
+#define define_id_show_func(name)				\
+static ssize_t name##_show(struct device *dev,			\
+		struct device_attribute *attr, char *buf)	\
+{								\
+	return sprintf(buf, "%d\n", topology_##name(dev->id));	\
+}
+
+#define define_siblings_show_map(name, mask)				\
+static ssize_t name##_show(struct device *dev,				\
+			   struct device_attribute *attr, char *buf)	\
+{									\
+	return cpumap_print_to_pagebuf(false, buf, topology_##mask(dev->id));\
+}
+
+#define define_siblings_show_list(name, mask)				\
+static ssize_t name##_list_show(struct device *dev,			\
+				struct device_attribute *attr,		\
+				char *buf)				\
+{									\
+	return cpumap_print_to_pagebuf(true, buf, topology_##mask(dev->id));\
+}
+
+#define define_siblings_show_func(name, mask)	\
+	define_siblings_show_map(name, mask);	\
+	define_siblings_show_list(name, mask)
+
+define_id_show_func(physical_package_id);
+static DEVICE_ATTR_RO(physical_package_id);
+
+define_id_show_func(core_id);
+static DEVICE_ATTR_RO(core_id);
+
+define_siblings_show_func(thread_siblings, sibling_cpumask);
+static DEVICE_ATTR_RO(thread_siblings);
+static DEVICE_ATTR_RO(thread_siblings_list);
+
+define_siblings_show_func(core_siblings, core_cpumask);
+static DEVICE_ATTR_RO(core_siblings);
+static DEVICE_ATTR_RO(core_siblings_list);
+
+#ifdef CONFIG_SCHED_BOOK
+define_id_show_func(book_id);
+static DEVICE_ATTR_RO(book_id);
+define_siblings_show_func(book_siblings, book_cpumask);
+static DEVICE_ATTR_RO(book_siblings);
+static DEVICE_ATTR_RO(book_siblings_list);
+#endif
+
+#ifdef CONFIG_SCHED_DRAWER
+define_id_show_func(drawer_id);
+static DEVICE_ATTR_RO(drawer_id);
+define_siblings_show_func(drawer_siblings, drawer_cpumask);
+static DEVICE_ATTR_RO(drawer_siblings);
+static DEVICE_ATTR_RO(drawer_siblings_list);
+#endif
+
+static struct attribute *topology_attrs[] = {
+	&dev_attr_physical_package_id.attr,
+	&dev_attr_core_id.attr,
+	&dev_attr_thread_siblings.attr,
+	&dev_attr_thread_siblings_list.attr,
+	&dev_attr_core_siblings.attr,
+	&dev_attr_core_siblings_list.attr,
+#ifdef CONFIG_SCHED_BOOK
+	&dev_attr_book_id.attr,
+	&dev_attr_book_siblings.attr,
+	&dev_attr_book_siblings_list.attr,
+#endif
+#ifdef CONFIG_SCHED_DRAWER
+	&dev_attr_drawer_id.attr,
+	&dev_attr_drawer_siblings.attr,
+	&dev_attr_drawer_siblings_list.attr,
+#endif
+	NULL
+};
+
+static struct attribute_group topology_attr_group = {
+	.attrs = topology_attrs,
+	.name = "topology"
+};
+
+/* Add/Remove cpu_topology interface for CPU device */
+static int topology_add_dev(unsigned int cpu)
+{
+	struct device *dev = get_cpu_device(cpu);
+
+	return sysfs_create_group(&dev->kobj, &topology_attr_group);
+}
+
+static void topology_remove_dev(unsigned int cpu)
+{
+	struct device *dev = get_cpu_device(cpu);
+
+	sysfs_remove_group(&dev->kobj, &topology_attr_group);
+}
+
+static int topology_cpu_callback(struct notifier_block *nfb,
+				 unsigned long action, void *hcpu)
+{
+	unsigned int cpu = (unsigned long)hcpu;
+	int rc = 0;
+
+	switch (action) {
+	case CPU_UP_PREPARE:
+	case CPU_UP_PREPARE_FROZEN:
+		rc = topology_add_dev(cpu);
+		break;
+	case CPU_UP_CANCELED:
+	case CPU_UP_CANCELED_FROZEN:
+	case CPU_DEAD:
+	case CPU_DEAD_FROZEN:
+		topology_remove_dev(cpu);
+		break;
+	}
+	return notifier_from_errno(rc);
+}
+
+static int topology_sysfs_init(void)
+{
+	int cpu;
+	int rc = 0;
+
+	cpu_notifier_register_begin();
+
+	for_each_online_cpu(cpu) {
+		rc = topology_add_dev(cpu);
+		if (rc)
+			goto out;
+	}
+	__hotcpu_notifier(topology_cpu_callback, 0);
+
+out:
+	cpu_notifier_register_done();
+	return rc;
+}
+
+device_initcall(topology_sysfs_init);
+
 static const struct attribute_group *common_cpu_attr_groups[] = {
 #ifdef CONFIG_KEXEC
 	&crash_note_cpu_attr_group,
diff --git a/drivers/base/topology.c b/drivers/base/topology.c
deleted file mode 100644
index df3c97cb4c99..000000000000
--- a/drivers/base/topology.c
+++ /dev/null
@@ -1,168 +0,0 @@
-/*
- * driver/base/topology.c - Populate sysfs with cpu topology information
- *
- * Written by: Zhang Yanmin, Intel Corporation
- *
- * Copyright (C) 2006, Intel Corp.
- *
- * All rights reserved.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
- * NON INFRINGEMENT.  See the GNU General Public License for more
- * details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
- *
- */
-#include <linux/mm.h>
-#include <linux/cpu.h>
-#include <linux/module.h>
-#include <linux/hardirq.h>
-#include <linux/topology.h>
-
-#define define_id_show_func(name)				\
-static ssize_t name##_show(struct device *dev,			\
-		struct device_attribute *attr, char *buf)	\
-{								\
-	return sprintf(buf, "%d\n", topology_##name(dev->id));	\
-}
-
-#define define_siblings_show_map(name, mask)				\
-static ssize_t name##_show(struct device *dev,				\
-			   struct device_attribute *attr, char *buf)	\
-{									\
-	return cpumap_print_to_pagebuf(false, buf, topology_##mask(dev->id));\
-}
-
-#define define_siblings_show_list(name, mask)				\
-static ssize_t name##_list_show(struct device *dev,			\
-				struct device_attribute *attr,		\
-				char *buf)				\
-{									\
-	return cpumap_print_to_pagebuf(true, buf, topology_##mask(dev->id));\
-}
-
-#define define_siblings_show_func(name, mask)	\
-	define_siblings_show_map(name, mask);	\
-	define_siblings_show_list(name, mask)
-
-define_id_show_func(physical_package_id);
-static DEVICE_ATTR_RO(physical_package_id);
-
-define_id_show_func(core_id);
-static DEVICE_ATTR_RO(core_id);
-
-define_siblings_show_func(thread_siblings, sibling_cpumask);
-static DEVICE_ATTR_RO(thread_siblings);
-static DEVICE_ATTR_RO(thread_siblings_list);
-
-define_siblings_show_func(core_siblings, core_cpumask);
-static DEVICE_ATTR_RO(core_siblings);
-static DEVICE_ATTR_RO(core_siblings_list);
-
-#ifdef CONFIG_SCHED_BOOK
-define_id_show_func(book_id);
-static DEVICE_ATTR_RO(book_id);
-define_siblings_show_func(book_siblings, book_cpumask);
-static DEVICE_ATTR_RO(book_siblings);
-static DEVICE_ATTR_RO(book_siblings_list);
-#endif
-
-#ifdef CONFIG_SCHED_DRAWER
-define_id_show_func(drawer_id);
-static DEVICE_ATTR_RO(drawer_id);
-define_siblings_show_func(drawer_siblings, drawer_cpumask);
-static DEVICE_ATTR_RO(drawer_siblings);
-static DEVICE_ATTR_RO(drawer_siblings_list);
-#endif
-
-static struct attribute *default_attrs[] = {
-	&dev_attr_physical_package_id.attr,
-	&dev_attr_core_id.attr,
-	&dev_attr_thread_siblings.attr,
-	&dev_attr_thread_siblings_list.attr,
-	&dev_attr_core_siblings.attr,
-	&dev_attr_core_siblings_list.attr,
-#ifdef CONFIG_SCHED_BOOK
-	&dev_attr_book_id.attr,
-	&dev_attr_book_siblings.attr,
-	&dev_attr_book_siblings_list.attr,
-#endif
-#ifdef CONFIG_SCHED_DRAWER
-	&dev_attr_drawer_id.attr,
-	&dev_attr_drawer_siblings.attr,
-	&dev_attr_drawer_siblings_list.attr,
-#endif
-	NULL
-};
-
-static struct attribute_group topology_attr_group = {
-	.attrs = default_attrs,
-	.name = "topology"
-};
-
-/* Add/Remove cpu_topology interface for CPU device */
-static int topology_add_dev(unsigned int cpu)
-{
-	struct device *dev = get_cpu_device(cpu);
-
-	return sysfs_create_group(&dev->kobj, &topology_attr_group);
-}
-
-static void topology_remove_dev(unsigned int cpu)
-{
-	struct device *dev = get_cpu_device(cpu);
-
-	sysfs_remove_group(&dev->kobj, &topology_attr_group);
-}
-
-static int topology_cpu_callback(struct notifier_block *nfb,
-				 unsigned long action, void *hcpu)
-{
-	unsigned int cpu = (unsigned long)hcpu;
-	int rc = 0;
-
-	switch (action) {
-	case CPU_UP_PREPARE:
-	case CPU_UP_PREPARE_FROZEN:
-		rc = topology_add_dev(cpu);
-		break;
-	case CPU_UP_CANCELED:
-	case CPU_UP_CANCELED_FROZEN:
-	case CPU_DEAD:
-	case CPU_DEAD_FROZEN:
-		topology_remove_dev(cpu);
-		break;
-	}
-	return notifier_from_errno(rc);
-}
-
-static int topology_sysfs_init(void)
-{
-	int cpu;
-	int rc = 0;
-
-	cpu_notifier_register_begin();
-
-	for_each_online_cpu(cpu) {
-		rc = topology_add_dev(cpu);
-		if (rc)
-			goto out;
-	}
-	__hotcpu_notifier(topology_cpu_callback, 0);
-
-out:
-	cpu_notifier_register_done();
-	return rc;
-}
-
-device_initcall(topology_sysfs_init);
-- 
1.7.9.3

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#1487548 — Re: [PATCH 1/2 v2] drivers/base: Combine topology.c and cpu.c

Fromkbuild test robot <lkp@intel.com>
Date2016-09-20 19:50 +0200
SubjectRe: [PATCH 1/2 v2] drivers/base: Combine topology.c and cpu.c
Message-ID<sjxl8-64Q-5@gated-at.bofh.it>
In reply to#1487432

[Multipart message — attachments visible in raw view] — view raw

Hi Prarit,

[auto build test ERROR on driver-core/driver-core-testing]
[also build test ERROR on v4.8-rc7 next-20160920]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
[Suggest to use git(>=2.9.0) format-patch --base=<commit> (or --base=auto for convenience) to record what (public, well-known) commit your patch series was built on]
[Check https://git-scm.com/docs/git-format-patch for more information]

url:    https://github.com/0day-ci/linux/commits/Prarit-Bhargava/cpu-hotplug-Preserve-topology-directory-after-soft-remove-event/20160920-233904
config: sparc64-defconfig (attached as .config)
compiler: sparc64-linux-gnu-gcc (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=sparc64 

All error/warnings (new ones prefixed by >>):

   In file included from arch/sparc/include/asm/topology.h:4:0,
                    from include/linux/topology.h:35,
                    from include/linux/gfp.h:8,
                    from include/linux/kmod.h:22,
                    from include/linux/module.h:13,
                    from drivers/base/cpu.c:6:
   drivers/base/cpu.c: In function 'physical_package_id_show':
>> arch/sparc/include/asm/topology_64.h:44:44: error: implicit declaration of function 'cpu_data' [-Werror=implicit-function-declaration]
    #define topology_physical_package_id(cpu) (cpu_data(cpu).proc_id)
                                               ^
>> drivers/base/cpu.c:188:30: note: in expansion of macro 'topology_physical_package_id'
     return sprintf(buf, "%d\n", topology_##name(dev->id)); \
                                 ^~~~~~~~~
>> drivers/base/cpu.c:210:1: note: in expansion of macro 'define_id_show_func'
    define_id_show_func(physical_package_id);
    ^~~~~~~~~~~~~~~~~~~
>> arch/sparc/include/asm/topology_64.h:44:57: error: request for member 'proc_id' in something not a structure or union
    #define topology_physical_package_id(cpu) (cpu_data(cpu).proc_id)
                                                            ^
>> drivers/base/cpu.c:188:30: note: in expansion of macro 'topology_physical_package_id'
     return sprintf(buf, "%d\n", topology_##name(dev->id)); \
                                 ^~~~~~~~~
>> drivers/base/cpu.c:210:1: note: in expansion of macro 'define_id_show_func'
    define_id_show_func(physical_package_id);
    ^~~~~~~~~~~~~~~~~~~
   drivers/base/cpu.c: In function 'core_id_show':
>> arch/sparc/include/asm/topology_64.h:45:47: error: request for member 'core_id' in something not a structure or union
    #define topology_core_id(cpu)   (cpu_data(cpu).core_id)
                                                  ^
>> drivers/base/cpu.c:188:30: note: in expansion of macro 'topology_core_id'
     return sprintf(buf, "%d\n", topology_##name(dev->id)); \
                                 ^~~~~~~~~
   drivers/base/cpu.c:213:1: note: in expansion of macro 'define_id_show_func'
    define_id_show_func(core_id);
    ^~~~~~~~~~~~~~~~~~~
>> drivers/base/cpu.c:186:10: warning: control reaches end of non-void function [-Wreturn-type]
      struct device_attribute *attr, char *buf) \
             ^
   drivers/base/cpu.c:213:1: note: in expansion of macro 'define_id_show_func'
    define_id_show_func(core_id);
    ^~~~~~~~~~~~~~~~~~~
   drivers/base/cpu.c: In function 'physical_package_id_show':
>> drivers/base/cpu.c:186:10: warning: control reaches end of non-void function [-Wreturn-type]
      struct device_attribute *attr, char *buf) \
             ^
>> drivers/base/cpu.c:210:1: note: in expansion of macro 'define_id_show_func'
    define_id_show_func(physical_package_id);
    ^~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/core_id +45 arch/sparc/include/asm/topology_64.h

f5e706ad include/asm-sparc/topology_64.h      Sam Ravnborg        2008-07-17  38  
f5e706ad include/asm-sparc/topology_64.h      Sam Ravnborg        2008-07-17  39  #include <asm-generic/topology.h>
f5e706ad include/asm-sparc/topology_64.h      Sam Ravnborg        2008-07-17  40  
f5e706ad include/asm-sparc/topology_64.h      Sam Ravnborg        2008-07-17  41  #endif /* !(CONFIG_NUMA) */
f5e706ad include/asm-sparc/topology_64.h      Sam Ravnborg        2008-07-17  42  
f5e706ad include/asm-sparc/topology_64.h      Sam Ravnborg        2008-07-17  43  #ifdef CONFIG_SMP
f5e706ad include/asm-sparc/topology_64.h      Sam Ravnborg        2008-07-17 @44  #define topology_physical_package_id(cpu)	(cpu_data(cpu).proc_id)
f5e706ad include/asm-sparc/topology_64.h      Sam Ravnborg        2008-07-17 @45  #define topology_core_id(cpu)			(cpu_data(cpu).core_id)
acc455cf arch/sparc/include/asm/topology_64.h chris hyser         2015-04-22  46  #define topology_core_cpumask(cpu)		(&cpu_core_sib_map[cpu])
06931e62 arch/sparc/include/asm/topology_64.h Bartosz Golaszewski 2015-05-26  47  #define topology_sibling_cpumask(cpu)		(&per_cpu(cpu_sibling_map, cpu))
f5e706ad include/asm-sparc/topology_64.h      Sam Ravnborg        2008-07-17  48  #endif /* CONFIG_SMP */

:::::: The code at line 45 was first introduced by commit
:::::: f5e706ad886b6a5eb59637830110b09ccebf01c5 sparc: join the remaining header files

:::::: TO: Sam Ravnborg <sam@ravnborg.org>
:::::: CC: David S. Miller <davem@davemloft.net>

---
0-DAY kernel test infrastructure                Open Source Technology Center
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#1487437 — [PATCH 2/2 v2] cpu hotplug: add CONFIG_PERMANENT_CPU_TOPOLOGY

FromPrarit Bhargava <prarit@redhat.com>
Date2016-09-20 17:30 +0200
Subject[PATCH 2/2 v2] cpu hotplug: add CONFIG_PERMANENT_CPU_TOPOLOGY
Message-ID<sjv9D-4MD-29@gated-at.bofh.it>
In reply to#1487427
The information in /sys/devices/system/cpu/cpuX/topology
directory is useful for userspace monitoring applications and in-tree
utilities like cpupower & turbostat.

When down'ing a thread the /sys/devices/system/cpu/cpuX/topology directory is
removed during the CPU_DEAD hotplug callback in the kernel.  The problem
with this model is that the thread's core has not been physically removed
and the data in the topology directory is still valid and the core's
location is now lost to userspace.

This patch adds CONFIG_PERMANENT_CPU_TOPOLOGY, and is Y by default for
x86, an N for all other arches.  When enabled the kernel is modified so
that the topology directory is added to the core cpu sysfs files so that
the topology directory exists while the CPU is physically present.  When
disabled, the behavior of the current kernel is maintained (that is, the
topology directory is removed on a soft down and added on an soft up of a
thread).

Adding CONFIG_PERMANENT_CPU_TOPOLOGY may require additional architecture
so that the cpumask data the CPU's topology is not cleared during a CPU
down.

Before patch:

[root@hp-z620-01 ~]# grep ^ /sys/devices/system/cpu/cpu10/topology/*
/sys/devices/system/cpu/cpu10/topology/core_id:3
/sys/devices/system/cpu/cpu10/topology/core_siblings:ffff
/sys/devices/system/cpu/cpu10/topology/core_siblings_list:0-15
/sys/devices/system/cpu/cpu10/topology/physical_package_id:0
/sys/devices/system/cpu/cpu10/topology/thread_siblings:0404
/sys/devices/system/cpu/cpu10/topology/thread_siblings_list:2,10

Down a cpu

[root@hp-z620-01 ~]# echo 0 > /sys/devices/system/cpu/cpu10/online

[root@hp-z620-01 ~]# ls /sys/devices/system/cpu/cpu10/topology
ls: cannot access topology: No such file or directory

After patch:

[root@hp-z620-01 ~]# grep ^ /sys/devices/system/cpu/cpu10/topology/*
/sys/devices/system/cpu/cpu10/topology/core_id:3
/sys/devices/system/cpu/cpu10/topology/core_siblings:ffff
/sys/devices/system/cpu/cpu10/topology/core_siblings_list:0-15
/sys/devices/system/cpu/cpu10/topology/physical_package_id:0
/sys/devices/system/cpu/cpu10/topology/thread_siblings:0404
/sys/devices/system/cpu/cpu10/topology/thread_siblings_list:2,10

Down a cpu

[root@hp-z620-01 ~]# echo 0 > /sys/devices/system/cpu/cpu10/online

[root@hp-z620-01 ~]# grep ^ /sys/devices/system/cpu/cpu10/topology/*
/sys/devices/system/cpu/cpu10/topology/core_id:3
/sys/devices/system/cpu/cpu10/topology/core_siblings:0000
/sys/devices/system/cpu/cpu10/topology/core_siblings_list:
/sys/devices/system/cpu/cpu10/topology/physical_package_id:0
/sys/devices/system/cpu/cpu10/topology/thread_siblings:0000
/sys/devices/system/cpu/cpu10/topology/thread_siblings_list:

I did some testing with and without BOOTPARAM_HOTPLUG_CPU0 enabled,
and up'd and down'd threads in sequence, randomly, by thread group, by
socket group and didn't see any issues.

core_siblings and thread_siblings are "numa siblings that are online"
and "thread siblings that are online" and are used as such within the kernel.
They must be zero'd out when the thread is offline.

CONFIG_PERMANENT_CPU_TOPOLOGY=y changes the lifetime of the topology
directory from existing when a thread is online to when a thread is
created and destroyed.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Len Brown <len.brown@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
---
 arch/x86/kernel/smpboot.c |    3 ---
 drivers/base/Kconfig      |   12 ++++++++++++
 drivers/base/cpu.c        |    8 ++++++++
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 4296beb8fdd3..ae82f8f45b61 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1472,7 +1472,6 @@ static void recompute_smt_state(void)
 static void remove_siblinginfo(int cpu)
 {
 	int sibling;
-	struct cpuinfo_x86 *c = &cpu_data(cpu);
 
 	for_each_cpu(sibling, topology_core_cpumask(cpu)) {
 		cpumask_clear_cpu(cpu, topology_core_cpumask(sibling));
@@ -1490,8 +1489,6 @@ static void remove_siblinginfo(int cpu)
 	cpumask_clear(cpu_llc_shared_mask(cpu));
 	cpumask_clear(topology_sibling_cpumask(cpu));
 	cpumask_clear(topology_core_cpumask(cpu));
-	c->phys_proc_id = 0;
-	c->cpu_core_id = 0;
 	cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
 	recompute_smt_state();
 }
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index 98504ec99c7d..b3935a272c3c 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -324,4 +324,16 @@ config CMA_ALIGNMENT
 
 endif
 
+config PERMANENT_CPU_TOPOLOGY
+	bool "Permanent CPU Topology"
+	depends on HOTPLUG_CPU
+	def_bool y if X86_64
+	help
+	  This option configures CPU topology to be permanent for the lifetime
+	  of the CPU (until it is physically removed).  Selecting Y here
+	  results in the kernel reporting the physical location for offlined
+	  CPUs.
+
+	  If unsure, leave the default value as is.
+
 endmenu
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index c59cecbb651a..e4e5d0cfe363 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -262,6 +262,7 @@ static struct attribute_group topology_attr_group = {
 	.name = "topology"
 };
 
+#ifndef CONFIG_PERMANENT_CPU_TOPOLOGY
 /* Add/Remove cpu_topology interface for CPU device */
 static int topology_add_dev(unsigned int cpu)
 {
@@ -318,11 +319,15 @@ out:
 }
 
 device_initcall(topology_sysfs_init);
+#endif
 
 static const struct attribute_group *common_cpu_attr_groups[] = {
 #ifdef CONFIG_KEXEC
 	&crash_note_cpu_attr_group,
 #endif
+#ifdef CONFIG_PERMANENT_CPU_TOPOLOGY
+	&topology_attr_group,
+#endif
 	NULL
 };
 
@@ -330,6 +335,9 @@ static const struct attribute_group *hotplugable_cpu_attr_groups[] = {
 #ifdef CONFIG_KEXEC
 	&crash_note_cpu_attr_group,
 #endif
+#ifdef CONFIG_PERMANENT_CPU_TOPOLOGY
+	&topology_attr_group,
+#endif
 	NULL
 };
 
-- 
1.7.9.3

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