linux-kernel - Re: [smp] a32a4d8a81: netperf.Throughput

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Message-ID: <CDFF26F9-A748-403C-86B2-4511DD6B1833@vmware.com>
Date:   Wed, 19 May 2021 19:31:16 +0000
From:   Nadav Amit <namit@...are.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     kernel test robot <oliver.sang@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "lkp@...ts.01.org" <lkp@...ts.01.org>,
        kernel test robot <lkp@...el.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "feng.tang@...el.com" <feng.tang@...el.com>,
        "zhengjun.xing@...el.com" <zhengjun.xing@...el.com>
Subject: Re: [smp]  a32a4d8a81:  netperf.Throughput_tps -2.1% regression



> On May 19, 2021, at 11:38 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> On Wed, May 19, 2021 at 06:17:35PM +0000, Nadav Amit wrote:
>>>     1287 ± 42%     +75.3%       2256 ± 14%  interrupts.CPU111.CAL:Function_call_interrupts
>>>     1326 ± 43%     +71.0%       2267 ± 13%  interrupts.CPU119.CAL:Function_call_interrupts
>>>     1300 ± 45%     +75.9%       2287 ± 37%  interrupts.CPU120.CAL:Function_call_interrupts
>>>     1299 ± 45%     +60.1%       2081 ± 28%  interrupts.CPU128.CAL:Function_call_interrupts
>>>     1305 ± 45%     +61.7%       2110 ± 29%  interrupts.CPU131.CAL:Function_call_interrupts
>>>     1299 ± 45%     +61.8%       2102 ± 28%  interrupts.CPU139.CAL:Function_call_interrupts
>>>    66.67 ±133%     -97.2%       1.83 ±155%  interrupts.CPU14.TLB:TLB_shootdowns
>>>     1299 ± 45%    +107.8%       2700 ± 33%  interrupts.CPU142.CAL:Function_call_interrupts
>>>   301.83 ±128%     -95.6%      13.17 ±140%  interrupts.CPU149.RES:Rescheduling_interrupts
>>>   389.17 ± 89%     -73.5%     103.17 ± 35%  interrupts.CPU164.NMI:Non-maskable_interrupts
>>>   389.17 ± 89%     -73.5%     103.17 ± 35%  interrupts.CPU164.PMI:Performance_monitoring_interrupts
>>>     1299 ± 45%     +60.2%       2081 ± 28%  interrupts.CPU35.CAL:Function_call_interrupts
>>>     1244 ± 50%     +66.8%       2076 ± 27%  interrupts.CPU45.CAL:Function_call_interrupts
>>>     1300 ± 44%     +59.5%       2075 ± 28%  interrupts.CPU46.CAL:Function_call_interrupts
>>>     1.50 ± 63%   +1422.2%      22.83 ±167%  interrupts.CPU47.RES:Rescheduling_interrupts
>>>   467.33 ± 85%     -64.6%     165.67 ± 74%  interrupts.CPU58.NMI:Non-maskable_interrupts
>>>   467.33 ± 85%     -64.6%     165.67 ± 74%  interrupts.CPU58.PMI:Performance_monitoring_interrupts
>>>   306.67 ± 75%     -59.9%     122.83 ± 16%  interrupts.CPU68.NMI:Non-maskable_interrupts
>>>   306.67 ± 75%     -59.9%     122.83 ± 16%  interrupts.CPU68.PMI:Performance_monitoring_interrupts
>>>     1131 ± 27%     +61.2%       1822 ± 35%  interrupts.CPU85.CAL:Function_call_interrupts
>>>     1180 ± 31%     +79.6%       2119 ± 24%  interrupts.CPU86.CAL:Function_call_interrupts
>>> 
> 
> It looks to be sending *waay* more call IPIs, did we mess up the mask or
> loose an optimization somewhere?
> 
> I'll go read the commit again…

As you know, I did mess up by calling arch_send_call_function_single_ipi()
instead of smp_call_function_single(), which could explain the extra IPIs.
But that was resolved by your subsequent patch.

For me, what stands out is the time in C1 spent after the patch.

I will try to reproduce the issue to figure it out, since so far I could
not find an error in the code.


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