Re: [PATCH v2 0/4] mm: arm64: bring up BATCHED_UNMAP_TLB_FLUSH

Xin Hao
2022-07-14T03:29:08Z

Hi barry.

I do some test on Kunpeng arm64 machine use Unixbench.

The test  result as below.

One core, we can see the performance improvement above +30%.
./Run -c 1 -i 1 shell1
w/o
System Benchmarks Partial Index              BASELINE RESULT INDEX
Shell Scripts (1 concurrent)                     42.4 5481.0 1292.7
========
System Benchmarks Index Score (Partial Only)                         1292.7

w/
System Benchmarks Partial Index              BASELINE RESULT INDEX
Shell Scripts (1 concurrent)                     42.4 6974.6 1645.0
========
System Benchmarks Index Score (Partial Only)                         1645.0

But with whole cores, there have little performance degradation above -5%

./Run -c 96 -i 1 shell1
w/o
Shell Scripts (1 concurrent)                  80765.5 lpm   (60.0 s, 1
samples)
System Benchmarks Partial Index              BASELINE RESULT INDEX
Shell Scripts (1 concurrent)                     42.4 80765.5 19048.5
========
System Benchmarks Index Score (Partial Only)                        19048.5

w
Shell Scripts (1 concurrent)                  76333.6 lpm   (60.0 s, 1
samples)
System Benchmarks Partial Index              BASELINE RESULT INDEX
Shell Scripts (1 concurrent)                     42.4 76333.6 18003.2
========
System Benchmarks Index Score (Partial Only)                        18003.2

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

After discuss with you, and do some changes in the patch.

ndex a52381a680db..1ecba81f1277 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -727,7 +727,11 @@ void flush_tlb_batched_pending(struct mm_struct *mm)
int flushed = batch >> TLB_FLUSH_BATCH_FLUSHED_SHIFT;

if (pending != flushed) {
+#ifdef CONFIG_ARCH_HAS_MM_CPUMASK
flush_tlb_mm(mm);
+#else
+ dsb(ish);
+#endif
/*
* If the new TLB flushing is pending during flushing, leave
* mm->tlb_flush_batched as is, to avoid losing flushing.

there have a performance improvement with whole cores, above +30%

./Run -c 96 -i 1 shell1
96 CPUs in system; running 96 parallel copies of tests

Shell Scripts (1 concurrent)                 109229.0 lpm   (60.0 s, 1 samples)
System Benchmarks Partial Index              BASELINE       RESULT    INDEX
Shell Scripts (1 concurrent)                     42.4     109229.0  25761.6
========
System Benchmarks Index Score (Partial Only)                        25761.6

Tested-by: Xin Hao<xhao@linux.alibaba.com>

Looking forward to your next version patch.

On 7/11/22 11:46 AM, Barry Song wrote:
> Though ARM64 has the hardware to do tlb shootdown, the hardware
> broadcasting is not free.
> A simplest micro benchmark shows even on snapdragon 888 with only
> 8 cores, the overhead for ptep_clear_flush is huge even for paging
> out one page mapped by only one process:
> 5.36% a.out [kernel.kallsyms] [k] ptep_clear_flush
>
> While pages are mapped by multiple processes or HW has more CPUs,
> the cost should become even higher due to the bad scalability of
> tlb shootdown.
>
> The same benchmark can result in 16.99% CPU consumption on ARM64
> server with around 100 cores according to Yicong's test on patch
> 4/4.
>
> This patchset leverages the existing BATCHED_UNMAP_TLB_FLUSH by
> 1. only send tlbi instructions in the first stage -
> arch_tlbbatch_add_mm()
> 2. wait for the completion of tlbi by dsb while doing tlbbatch
> sync in arch_tlbbatch_flush()
> My testing on snapdragon shows the overhead of ptep_clear_flush
> is removed by the patchset. The micro benchmark becomes 5% faster
> even for one page mapped by single process on snapdragon 888.
>
>
> -v2:
> 1. Collected Yicong's test result on kunpeng920 ARM64 server;
> 2. Removed the redundant vma parameter in arch_tlbbatch_add_mm()
> according to the comments of Peter Zijlstra and Dave Hansen
> 3. Added ARCH_HAS_MM_CPUMASK rather than checking if mm_cpumask
> is empty according to the comments of Nadav Amit
>
> Thanks, Yicong, Peter, Dave and Nadav for your testing or reviewing
> , and comments.
>
> -v1:
> https://lore.kernel.org/lkml/20220707125242.425242-1-21cnbao@gmail.com/
>
> Barry Song (4):
> Revert "Documentation/features: mark BATCHED_UNMAP_TLB_FLUSH doesn't
> apply to ARM64"
> mm: rmap: Allow platforms without mm_cpumask to defer TLB flush
> mm: rmap: Extend tlbbatch APIs to fit new platforms
> arm64: support batched/deferred tlb shootdown during page reclamation
>
> Documentation/features/arch-support.txt | 1 -
> .../features/vm/TLB/arch-support.txt | 2 +-
> arch/arm/Kconfig | 1 +
> arch/arm64/Kconfig | 1 +
> arch/arm64/include/asm/tlbbatch.h | 12 ++++++++++
> arch/arm64/include/asm/tlbflush.h | 23 +++++++++++++++++--
> arch/loongarch/Kconfig | 1 +
> arch/mips/Kconfig | 1 +
> arch/openrisc/Kconfig | 1 +
> arch/powerpc/Kconfig | 1 +
> arch/riscv/Kconfig | 1 +
> arch/s390/Kconfig | 1 +
> arch/um/Kconfig | 1 +
> arch/x86/Kconfig | 1 +
> arch/x86/include/asm/tlbflush.h | 3 ++-
> mm/Kconfig | 3 +++
> mm/rmap.c | 14 +++++++----
> 17 files changed, 59 insertions(+), 9 deletions(-)
> create mode 100644 arch/arm64/include/asm/tlbbatch.h
>
--
Best Regards!
Xin Hao