This is a note to let you know that I've just added the patch titled
sched/x86: Optimize switch_mm() for multi-threaded workloads
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-x86-optimize-switch_mm-for-multi-threaded-workloads.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 8f898fbbe5ee5e20a77c4074472a1fd088dc47d1 Mon Sep 17 00:00:00 2001
From: Rik van Riel <riel@xxxxxxxxxx>
Date: Wed, 31 Jul 2013 22:14:21 -0400
Subject: sched/x86: Optimize switch_mm() for multi-threaded workloads
From: Rik van Riel <riel@xxxxxxxxxx>
commit 8f898fbbe5ee5e20a77c4074472a1fd088dc47d1 upstream.
Dick Fowles, Don Zickus and Joe Mario have been working on
improvements to perf, and noticed heavy cache line contention
on the mm_cpumask, running linpack on a 60 core / 120 thread
system.
The cause turned out to be unnecessary atomic accesses to the
mm_cpumask. When in lazy TLB mode, the CPU is only removed from
the mm_cpumask if there is a TLB flush event.
Most of the time, no such TLB flush happens, and the kernel
skips the TLB reload. It can also skip the atomic memory
set & test.
Here is a summary of Joe's test results:
* The __schedule function dropped from 24% of all program cycles down
to 5.5%.
* The cacheline contention/hotness for accesses to that bitmask went
from being the 1st/2nd hottest - down to the 84th hottest (0.3% of
all shared misses which is now quite cold)
* The average load latency for the bit-test-n-set instruction in
__schedule dropped from 10k-15k cycles down to an average of 600 cycles.
* The linpack program results improved from 133 GFlops to 144 GFlops.
Peak GFlops rose from 133 to 153.
Reported-by: Don Zickus <dzickus@xxxxxxxxxx>
Reported-by: Joe Mario <jmario@xxxxxxxxxx>
Tested-by: Joe Mario <jmario@xxxxxxxxxx>
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Reviewed-by: Paul Turner <pjt@xxxxxxxxxx>
Acked-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20130731221421.616d3d20@xxxxxxxxxxxxxxxxxxxxx
[ Made the comments consistent around the modified code. ]
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/mmu_context.h | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -45,22 +45,28 @@ static inline void switch_mm(struct mm_s
/* Re-load page tables */
load_cr3(next->pgd);
- /* stop flush ipis for the previous mm */
+ /* Stop flush ipis for the previous mm */
cpumask_clear_cpu(cpu, mm_cpumask(prev));
- /*
- * load the LDT, if the LDT is different:
- */
+ /* Load the LDT, if the LDT is different: */
if (unlikely(prev->context.ldt != next->context.ldt))
load_LDT_nolock(&next->context);
}
#ifdef CONFIG_SMP
- else {
+ else {
this_cpu_write(cpu_tlbstate.state, TLBSTATE_OK);
BUG_ON(this_cpu_read(cpu_tlbstate.active_mm) != next);
- if (!cpumask_test_and_set_cpu(cpu, mm_cpumask(next))) {
- /* We were in lazy tlb mode and leave_mm disabled
+ if (!cpumask_test_cpu(cpu, mm_cpumask(next))) {
+ /*
+ * On established mms, the mm_cpumask is only changed
+ * from irq context, from ptep_clear_flush() while in
+ * lazy tlb mode, and here. Irqs are blocked during
+ * schedule, protecting us from simultaneous changes.
+ */
+ cpumask_set_cpu(cpu, mm_cpumask(next));
+ /*
+ * We were in lazy tlb mode and leave_mm disabled
* tlb flush IPI delivery. We must reload CR3
* to make sure to use no freed page tables.
*/
Patches currently in stable-queue which might be from riel@xxxxxxxxxx are
queue-3.10/sched-x86-optimize-switch_mm-for-multi-threaded-workloads.patch
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