Re: [PATCH v2 0/4] mm: arm64: bring up BATCHED_UNMAP_TLB_FLUSH
From: xhao
Date: Sat Jul 23 2022 - 05:23:02 EST
On 7/20/22 7:18 PM, Barry Song wrote:
On Tue, Jul 19, 2022 at 1:28 AM Yicong Yang <yangyicong@xxxxxxxxxx> wrote:
On 2022/7/14 12:51, Barry Song wrote:
On Thu, Jul 14, 2022 at 3:29 PM Xin Hao <xhao@xxxxxxxxxxxxxxxxx> wrote:
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.
./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.
./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?
Oh, my fault, I do the test is not based on the lastest upstream kernel, there maybe some impact here,
i will do a new test on the lastest kernel.
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
--
Best Regards!
Xin Hao