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

[xhao@linux.alibaba.com]

On 7/20/22 7:18 PM, Barry Song wrote:
> On Tue, Jul 19, 2022 at 1:28 AM Yicong Yang <yangyicong@huawei.com> wrote:
>> On 2022/7/14 12:51, Barry Song wrote:
>>> On Thu, Jul 14, 2022 at 3:29 PM Xin Hao <xhao@linux.alibaba.com> 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