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

On Tue, Jul 19, 2022 at 1:28 AM Yicong Yang [off-list ref] wrote:

On 2022/7/14 12:51, Barry Song wrote:

quoted

On Thu, Jul 14, 2022 at 3:29 PM Xin Hao [off-list ref] wrote:

quoted

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%.

I am really pleased to see the 30%+ improvement on unixbench on single core.

quoted

./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%

That is sad as we might get more concurrency between mprotect(), madvise(),
mremap(), zap_pte_range() and the deferred tlbi.

quoted

./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

i was guessing the problem might be flush_tlb_batched_pending()
so i asked you to change this to verify my guess.

flush_tlb_batched_pending() looks like the critical path for this issue then the code
above can mitigate this.

I cannot reproduce this on a 2P 128C Kunpeng920 server. The kernel is based on the
v5.19-rc6 and unixbench of version 5.1.3. The result of `./Run -c 128 -i 1 shell1` is:
      iter-1      iter-2     iter-3
w/o  17708.1     17637.1    17630.1
w    17766.0     17752.3    17861.7

And flush_tlb_batched_pending()isn't the hot spot with the patch:
   7.00%  sh        [kernel.kallsyms]      [k] ptep_clear_flush
   4.17%  sh        [kernel.kallsyms]      [k] ptep_set_access_flags
   2.43%  multi.sh  [kernel.kallsyms]      [k] ptep_clear_flush
   1.98%  sh        [kernel.kallsyms]      [k] _raw_spin_unlock_irqrestore
   1.69%  sh        [kernel.kallsyms]      [k] next_uptodate_page
   1.66%  sort      [kernel.kallsyms]      [k] ptep_clear_flush
   1.56%  multi.sh  [kernel.kallsyms]      [k] ptep_set_access_flags
   1.27%  sh        [kernel.kallsyms]      [k] page_counter_cancel
   1.11%  sh        [kernel.kallsyms]      [k] page_remove_rmap
   1.06%  sh        [kernel.kallsyms]      [k] perf_event_alloc

Hi Xin Hao,

I'm not sure the test setup as well as the config is same with yours. (96C vs 128C
should not be the reason I think). Did you check that the 5% is a fluctuation or
not? It'll be helpful if more information provided for reproducing this issue.

Thanks.

I guess that is because  "./Run -c 1 -i 1 shell1" isn't an application
stressed on
memory. Hi Xin, in what kinds of configurations can we reproduce your test
result?

As I suppose tlbbatch will mainly affect the performance of user scenarios
which require memory page-out/page-in like reclaiming file/anon pages.
"./Run -c 1 -i 1 shell1" on a system with sufficient free memory won't be
affected by tlbbatch at all, I believe.

Thanks
Barry