3.11-stable review patch. If anyone has any objections, please let me know. ------------------ 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. */ -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html