Re: [LKP] [btrfs] 8d47a0d8f7: fio.write_bw_MBps -28.6% regression

[Xing Zhengjun <zhengjun.xing@linux.intel.com>]

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This regression happened on "lkp-hsw-ep2", but “lkp-hsw-ep2” has been 
removed from the LKP tbox, so we retest the regression on another tbox 
“lkp-hsw-ep4”, their hardware is almost the same, "72 threads Intel(R) 
Xeon(R) CPU E5-2699 v3 @ 2.30GHz with 256G memory". The test result is 
in the attached file compare.txt. The regression is -6.7% for v5.6, the 
origin regression is -8.9%, it is not serious as it test on 
"lkp-hsw-ep2" before.


On 4/10/2020 6:14 PM, David Sterba wrote:
> On Fri, Apr 10, 2020 at 02:44:55PM +0800, Qu Wenruo wrote:
>> On 2020/4/10 下午2:34, Xing Zhengjun wrote:
>>> Hi Wenruo,
>>>
>>>     We test it in v5.6, the issue still exist, do you have time to take a
>>> look at this? Thanks.
>>
>> This is expected.
>>
>> The extra check brings new overhead mostly equal to another CRC32 run.
>>
>> We believe it's worthy, as our read time tree checker has exposed quite
>> some bit flip corruption.
> 
> The test probably runs on a PMEM device so there's no slowdown from the
> actual IO and the in-memory checks are measurable, though 28% is a lot,
> I'd expect something like 5-10% at most.
> 

-- 
Zhengjun Xing

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=========================================================================================
tbox_group/testcase/rootfs/kconfig/compiler/debug-setup/disk/fs/runtime/nr_task/time_based/rw/bs/ioengine/test_size/cpufreq_governor/ucode:
  lkp-hsw-ep4/fio-basic/debian-x86_64-20191114.cgz/x86_64-rhel-7.6/gcc-7/test/2pmem/btrfs/200s/50%/tb/randwrite/4k/libaio/100G/performance/0x43

commit: 
  ff2ac107fae2440b6877c615c0ac788d2a106ed7
  8d47a0d8f7947422dd359ac8e462687f81a7a137
  v5.6

ff2ac107fae2440b 8d47a0d8f7947422dd359ac8e46                        v5.6 
---------------- --------------------------- --------------------------- 
         %stddev     %change         %stddev     %change         %stddev
             \          |                \          |                \  
      0.44 ±  7%      -0.1        0.32 ±  4%      -0.1        0.36 ± 10%  fio.latency_1000ms%
      0.16 ± 11%      -0.1        0.03 ± 25%      -0.1        0.02 ±  8%  fio.latency_100ms%
      5.59 ±  3%      -0.0        5.59 ±  9%      +5.7       11.26 ± 15%  fio.latency_10ms%
     38.25            +1.7       39.92 ±  3%      +4.7       42.97        fio.latency_20ms%
      0.29 ±  4%      -0.1        0.16 ±  2%      -0.2        0.06 ± 14%  fio.latency_250ms%
      0.58 ± 17%      +0.1        0.66 ± 10%      -0.5        0.08 ±  6%  fio.latency_250us%
      0.17 ± 43%      +0.1        0.24 ± 34%      +0.2        0.40 ± 30%  fio.latency_2ms%
     44.24            -4.3       39.95            -4.2       39.99 ±  3%  fio.latency_4ms%
      0.03 ±  4%      +0.2        0.19 ±  3%      +0.1        0.16 ± 10%  fio.latency_500ms%
      8.56 ±  4%      +2.7       11.30 ±  8%      -6.2        2.35 ±  5%  fio.latency_50ms%
      0.03 ± 24%      +0.2        0.28            +0.4        0.45 ±  2%  fio.latency_750ms%
      0.11 ± 38%      -0.0        0.10 ± 31%      +0.3        0.41 ± 33%  fio.latency_750us%
  13682713            -9.0%   12457118            -6.7%   12764827        fio.workload
    266.36            -8.9%     242.70            -6.5%     248.99        fio.write_bw_MBps
  19966634            +3.1%   20578304            -9.2%   18131626        fio.write_clat_90%_us
  21976405            +3.2%   22675456           -12.3%   19267584        fio.write_clat_95%_us
  92798976 ±  5%    +124.1%   2.08e+08 ±  3%    +375.3%  4.411e+08 ±  2%  fio.write_clat_99%_us
  16353304            +9.7%   17942942            +7.0%   17500789        fio.write_clat_mean_us
  76828732            +0.4%   77132911            +6.9%   82135424 ±  2%  fio.write_clat_stddev
     68188            -8.9%      62131            -6.5%      63740        fio.write_iops
    523406            +9.7%     574400            +7.0%     560260        fio.write_slat_mean_us
  13649919            -3.8%   13133471            +7.9%   14729703        fio.write_slat_stddev