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| Started by | Thomas Gleixner <tglx@linutronix.de> |
|---|---|
| First post | 2016-05-05 21:10 +0200 |
| Last post | 2016-05-05 21:10 +0200 |
| Articles | 2 — 1 participant |
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[patch V2 0/7] Sebastian Andrzej Siewior <bigeasy@linutronix.de>, Linus Torvalds <torvalds@linux-foundation.org>, Darren Hart <darren@dvhart.com>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Michael Kerrisk <mtk.manpages@googlemail.com>, Davidlohr Bueso <dave@stgolabs.net>, Chris Mason <clm@fb.com>, Carlos O'Donell <carlos@redhat.com>, Torvald Riegel <triegel@redhat.com>, Eric Dumazet <edumazet@google.com> Thomas Gleixner <tglx@linutronix.de> - 2016-05-05 21:10 +0200
[patch V2 4/7] futex: Add sysctl knobs for process private hash Thomas Gleixner <tglx@linutronix.de> - 2016-05-05 21:10 +0200
| From | Thomas Gleixner <tglx@linutronix.de> |
|---|---|
| Date | 2016-05-05 21:10 +0200 |
| Subject | [patch V2 0/7] Sebastian Andrzej Siewior <bigeasy@linutronix.de>, Linus Torvalds <torvalds@linux-foundation.org>, Darren Hart <darren@dvhart.com>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Michael Kerrisk <mtk.manpages@googlemail.com>, Davidlohr Bueso <dave@stgolabs.net>, Chris Mason <clm@fb.com>, Carlos O'Donell <carlos@redhat.com>, Torvald Riegel <triegel@redhat.com>, Eric Dumazet <edumazet@google.com> |
| Message-ID | <rvwOS-5Wn-5@gated-at.bofh.it> |
The standard futex mechanism in the Linux kernel uses a global hash to store transient state. Collisions on that hash can lead to performance degradation and on real-time enabled kernels to unbound priority inversions. This new attempt to solve the issue does not require user space changes and operates transparently. On the first futex operation of a process the kernel allocates a hash private to the process. All process private futexes are hashed in this hash. Process shared futexes still use the global hash. For RT applications and pathological use cases a new futex op is provided which allows the application to preallocate and thereby size the process private hash. The last two patches add support to the perf futex-hash benchmark so test can be run on nodes and the preallocation sizing can be tested. The last patch contains a first update for the futex man page. The difference vs. V1 of this series is that it uses hash_long() now that the hash_64 implementation has been fixed in mainline. The performance numbers are more or less the same as with V1 [1]. Thanks, tglx [1] http://lkml.kernel.org/r/20160428161742.363543816@linutronix.de ---- Documentation/sysctl/kernel.txt | 17 +++ b/include/linux/futex_types.h | 12 ++ include/linux/futex.h | 39 +++++-- include/linux/mm_types.h | 4 include/uapi/linux/futex.h | 1 init/Kconfig | 4 kernel/fork.c | 3 kernel/futex.c | 215 +++++++++++++++++++++++++++++++++++++++- kernel/sysctl.c | 21 +++ tools/perf/bench/Build | 4 tools/perf/bench/futex-hash.c | 101 ++++++++++++++++-- tools/perf/bench/futex.h | 5 12 files changed, 403 insertions(+), 23 deletions(-)
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| From | Thomas Gleixner <tglx@linutronix.de> |
|---|---|
| Date | 2016-05-05 21:10 +0200 |
| Subject | [patch V2 4/7] futex: Add sysctl knobs for process private hash |
| Message-ID | <rvwOT-5Wn-35@gated-at.bofh.it> |
| In reply to | #1395306 |
From: Sebastian Siewior <bigeasy@linutronix.de>
To adjust the default hash size and the maximum hash size for process private
futexes we add the following sysctls:
futex_private_default_hash_bits:
Adjusts the default hash size (in bits) which is used for automatic hash
allocations on the first futex operation
futex_private_max_hash_bits:
Adjusts the maximum hash size (in bits). This limits the hash size which
can be preallocated by applications with the FUTEX_PREALLOC_HASH op.
Signed-off-by: Sebastian Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
Documentation/sysctl/kernel.txt | 17 +++++++++++++++++
include/linux/futex.h | 1 +
kernel/futex.c | 5 +++--
kernel/sysctl.c | 21 +++++++++++++++++++++
4 files changed, 42 insertions(+), 2 deletions(-)
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -29,6 +29,8 @@ Currently, these files might (depending
- core_pipe_limit
- core_uses_pid
- ctrl-alt-del
+- futex_private_default_hash_bits
+- futex_private_max_hash_bits
- dmesg_restrict
- domainname
- hostname
@@ -265,6 +267,21 @@ to decide what to do with it.
==============================================================
+futex_private_default_hash_bits:
+
+Adjusts the default hash size (in bits) which is used for
+automatic hash allocations on the first futex operation
+
+==============================================================
+
+futex_private_max_hash_bits:
+
+Adjusts the maximum hash size (in bits). This limits the hash
+size which can be preallocated by applications with the
+FUTEX_PREALLOC_HASH op.
+
+==============================================================
+
dmesg_restrict:
This toggle indicates whether unprivileged users are prevented
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -75,6 +75,7 @@ static inline void exit_pi_state_list(st
extern unsigned int futex_default_hash_bits;
extern unsigned int futex_max_hash_bits;
+extern unsigned int futex_sysmax_hash_bits;
extern void futex_mm_hash_exit(struct mm_struct *mm);
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -297,8 +297,9 @@ struct futex_hash_bucket {
#define FUTEX_DEF_HASH_BITS order_base_2(8UL)
#define FUTEX_MAX_HASH_BITS order_base_2(256UL)
-unsigned int futex_default_hash_bits = FUTEX_DEF_HASH_BITS;
-unsigned int futex_max_hash_bits = FUTEX_MAX_HASH_BITS;
+unsigned int futex_default_hash_bits = FUTEX_DEF_HASH_BITS;
+unsigned int futex_max_hash_bits = FUTEX_MAX_HASH_BITS;
+unsigned int __read_mostly futex_sysmax_hash_bits = FUTEX_MAX_HASH_BITS;
#else
static const unsigned int futex_default_hash_bits = 0;
#endif
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -65,6 +65,7 @@
#include <linux/sched/sysctl.h>
#include <linux/kexec.h>
#include <linux/bpf.h>
+#include <linux/futex.h>
#include <asm/uaccess.h>
#include <asm/processor.h>
@@ -593,6 +594,26 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec,
},
+#ifdef CONFIG_FUTEX_PRIVATE_HASH
+ {
+ .procname = "futex_private_default_hash_bits",
+ .data = &futex_default_hash_bits,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &two,
+ .extra2 = &futex_max_hash_bits,
+ },
+ {
+ .procname = "futex_private_max_hash_bits",
+ .data = &futex_max_hash_bits,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &futex_default_hash_bits,
+ .extra2 = &futex_sysmax_hash_bits,
+ },
+#endif
#ifdef CONFIG_FUNCTION_TRACER
{
.procname = "ftrace_enabled",
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