Re: [numa shrinker] 9b17c62382: -36.6% regression on sparse file copy

[Fengguang Wu <fengguang.wu@intel.com>]

Hi Dave,

On Wed, Jan 15, 2014 at 11:18:27AM +1100, Dave Chinner wrote:
> On Thu, Jan 09, 2014 at 10:57:15AM +0800, Fengguang Wu wrote:
> > Hi Dave,
> > 
> > As you suggested, I added tests for ext4 and btrfs, the results are
> > the same.
> > 
> > Then I tried running perf record for 10 seconds starting from 200s.
> > (The test runs for 410s). I see several warning messages and hope
> > they do not impact the accuracy too much:
> > 
> > [  252.608069] perf samples too long (2532 > 2500), lowering kernel.perf_event_max_sample_rate to 50000
> > [  252.608863] perf samples too long (2507 > 2500), lowering kernel.perf_event_max_sample_rate to 25000
> > [  252.609422] INFO: NMI handler (perf_event_nmi_handler) took too long to run: 1.389 msecs
> > 
> > Anyway the noticeable perf change are:
> > 
> > 1d3d4437eae1bb2  9b17c62382dd2e7507984b989  
> > ---------------  -------------------------  
> >      12.15 ~10%    +209.8%      37.63 ~ 2%  brickland2/debug2/vm-scalability/300s-btrfs-lru-file-readtwice
> >      12.88 ~16%    +189.4%      37.27 ~ 0%  brickland2/debug2/vm-scalability/300s-ext4-lru-file-readtwice
> >      15.24 ~ 9%    +146.0%      37.50 ~ 1%  brickland2/debug2/vm-scalability/300s-xfs-lru-file-readtwice
> >      40.27         +179.1%     112.40       TOTAL perf-profile.cpu-cycles._raw_spin_lock.grab_super_passive.super_cache_count.shrink_slab.do_try_to_free_pages
> > 
> > 1d3d4437eae1bb2  9b17c62382dd2e7507984b989  
> > ---------------  -------------------------  
> >      11.91 ~12%    +218.2%      37.89 ~ 2%  brickland2/debug2/vm-scalability/300s-btrfs-lru-file-readtwice
> >      12.47 ~16%    +200.3%      37.44 ~ 0%  brickland2/debug2/vm-scalability/300s-ext4-lru-file-readtwice
> >      15.36 ~11%    +145.4%      37.68 ~ 1%  brickland2/debug2/vm-scalability/300s-xfs-lru-file-readtwice
> >      39.73         +184.5%     113.01       TOTAL perf-profile.cpu-cycles._raw_spin_lock.put_super.drop_super.super_cache_count.shrink_slab
> > 
> > perf report for 9b17c62382dd2e7507984b989:
> > 
> > # Overhead          Command       Shared Object                                          Symbol
> > # ........  ...............  ..................  ..............................................
> > #
> >     77.74%               dd  [kernel.kallsyms]   [k] _raw_spin_lock                            
> >                          |
> >                          --- _raw_spin_lock
> >                             |          
> >                             |--47.65%-- grab_super_passive
> 
> Oh, it's superblock lock contention, probably caused by an increase
> in shrinker calls (i.e. per-node rather than global). I think we've
> seen this before - can you try the two patches from Tim Chen here:
> 
> https://lkml.org/lkml/2013/9/6/353
> https://lkml.org/lkml/2013/9/6/356
> 
> If they fix the problem, I'll get them into 3.14 and pushed back to
> the relevant stable kernels.

Yes, the two patches help a lot:

9b17c62382dd2e7  8401edd4b12960c703233f4ed
---------------  -------------------------  
   6748913 ~ 2%     +37.5%    9281049 ~ 1%  brickland2/debug2/vm-scalability/300s-btrfs-lru-file-readtwice
   8417200 ~ 0%     +56.5%   13172417 ~ 0%  brickland2/debug2/vm-scalability/300s-ext4-lru-file-readtwice
   8333983 ~ 1%     +56.9%   13078610 ~ 0%  brickland2/debug2/vm-scalability/300s-xfs-lru-file-readtwice
  23500096 ~ 1%     +51.2%   35532077 ~ 0%  TOTAL vm-scalability.throughput

They restore performance numbers back to 1d3d4437eae1bb2's level
(which is 9b17c62382's parent commit).

Thanks,
Fengguang

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