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[PATCH 4.12 22/27] sched/fair: Simplify wake_affine() for the single socket case

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4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rik van Riel <riel@redhat.com>

commit 7d894e6e34a5cdd12309c7e4a3f830277ad4b7bf upstream.

Then 'this_cpu' and 'prev_cpu' are in the same socket, select_idle_sibling()
will do its thing regardless of the return value of wake_affine().

Just return true and don't look at all the other things.

Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: jhladky@redhat.com
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20170623165530.22514-3-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/sched/fair.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5399,6 +5399,13 @@ static int wake_affine(struct sched_doma
 	this_load = target_load(this_cpu, idx);
 
 	/*
+	 * Common case: CPUs are in the same socket, and select_idle_sibling()
+	 * will do its thing regardless of what we return:
+	 */
+	if (cpus_share_cache(prev_cpu, this_cpu))
+		return true;
+
+	/*
 	 * If sync wakeup then subtract the (maximum possible)
 	 * effect of the currently running task from the load
 	 * of the current CPU:
@@ -5986,11 +5993,15 @@ select_task_rq_fair(struct task_struct *
 
 	if (affine_sd) {
 		sd = NULL; /* Prefer wake_affine over balance flags */
-		if (cpu != prev_cpu && wake_affine(affine_sd, p, prev_cpu, sync))
+		if (cpu == prev_cpu)
+			goto pick_cpu;
+
+		if (wake_affine(affine_sd, p, prev_cpu, sync))
 			new_cpu = cpu;
 	}
 
 	if (!sd) {
+ pick_cpu:
 		if (sd_flag & SD_BALANCE_WAKE) /* XXX always ? */
 			new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
 

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[PATCH 4.12 00/27] 4.12.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:20 +0200
  [PATCH 4.12 14/27] tpm: Issue a TPM2_Shutdown for TPM2 devices. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:20 +0200
  [PATCH 4.12 26/27] xen: avoid deadlock in xenbus driver Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:20 +0200
  [PATCH 4.12 05/27] usb: usbip: set buffer pointers to NULL after free Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:20 +0200
  [PATCH 4.12 02/27] RDMA/uverbs: Check port number supplied by user verbs cmds Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:20 +0200
  [PATCH 4.12 19/27] sched/core: Implement new approach to scale select_idle_cpu() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:20 +0200
  [PATCH 4.12 01/27] driver core: platform: fix race condition with driver_override Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:20 +0200
  [PATCH 4.12 06/27] Add USB quirk for HVR-950q to avoid intermittent device resets Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:20 +0200
  [PATCH 4.12 25/27] sched/numa: Hide numa_wake_affine() from UP build Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:30 +0200
  [PATCH 4.12 17/27] x86/uaccess: Optimize copy_user_enhanced_fast_string() for short strings Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:30 +0200
  [PATCH 4.12 04/27] USB: serial: cp210x: add ID for CEL EM3588 USB ZigBee stick Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 13/27] Add "shutdown" to "struct class". Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 11/27] xhci: Limit USB2 port wake support for AMD Promontory hosts Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 18/27] sched/fair, cpumask: Export for_each_cpu_wrap() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 23/27] sched/numa: Implement NUMA node level wake_affine() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 24/27] sched/fair: Remove effective_load() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 15/27] tpm: fix a kernel memory leak in tpm-sysfs.c Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 20/27] sched/numa: Use down_read_trylock() for the mmap_sem Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 08/27] USB: core: fix device node leak Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 12/27] gfs2: Fix glock rhashtable rcu bug Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 03/27] usb: dwc3: replace %p with %pK Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 27/27] crypto: drbg - Fixes panic in wait_for_completion call Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 22/27] sched/fair: Simplify wake_affine() for the single socket case Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  [PATCH 4.12 07/27] usb: Fix typo in the definition of Endpoint[out]Request Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-10 19:40 +0200
  Re: [PATCH 4.12 00/27] 4.12.1-stable review Guenter Roeck <linux@roeck-us.net> - 2017-07-11 03:30 +0200
    Re: [PATCH 4.12 00/27] 4.12.1-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-07-11 11:50 +0200

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