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

[Xin Hao]

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 at 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