netdev - Re: [MM PATCH V4.1 5/6] slub: support for bulk free with SLUB freelists

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Date:	Wed, 7 Oct 2015 14:31:20 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	linux-mm@...ck.org, netdev@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	brouer@...hat.com
Subject: Re: [MM PATCH V4.1 5/6] slub: support for bulk free with SLUB
 freelists

On Tue, 6 Oct 2015 01:07:03 +0200
Jesper Dangaard Brouer <brouer@...hat.com> wrote:

> (trimmed Cc list a little)
> 
> On Mon, 5 Oct 2015 14:20:45 -0700 Andi Kleen <ak@...ux.intel.com> wrote:
> 
> > > My only problem left, is I want a perf measurement that pinpoint these
> > > kind of spots.  The difference in L1-icache-load-misses were significant
> > > (1,278,276 vs 2,719,158).  I tried to somehow perf record this with
> > > different perf events without being able to pinpoint the location (even
> > > though I know the spot now).  Even tried Andi's ocperf.py... maybe he
> > > will know what event I should try?
> > 
> > Run pmu-tools toplev.py -l3 with --show-sample. It tells you what the
> > bottle neck is and what to sample for if there is a suitable event and
> > even prints the command line.
> > 
> > https://github.com/andikleen/pmu-tools/wiki/toplev-manual#sampling-with-toplev
> > 
> 
> My result from (IP-forward flow hitting CPU 0):
>  $ sudo ./toplev.py -I 1000 -l3 -a --show-sample --core C0
> 
> So, what does this tell me?:
>
>  C0    BAD     Bad_Speculation:                                 0.00 % [  5.50%]
>  C0    BE      Backend_Bound:                                 100.00 % [  5.50%]
>  C0    BE/Mem  Backend_Bound.Memory_Bound:                     53.06 % [  5.50%]
>  C0    BE/Core Backend_Bound.Core_Bound:                       46.94 % [  5.50%]
>  C0-T0 FE      Frontend_Bound.Frontend_Latency.Branch_Resteers: 5.42 % [  5.50%]
>  C0-T0 BE/Mem  Backend_Bound.Memory_Bound.L1_Bound:            54.51 % [  5.50%]
>  C0-T0 BE/Core Backend_Bound.Core_Bound.Ports_Utilization:     20.99 % [  5.60%]
>  C0-T0         CPU utilization: 1.00 CPUs   	[100.00%]
>  C0-T1 FE      Frontend_Bound.Frontend_Latency.Branch_Resteers: 6.04 % [  5.50%]
>  C0-T1         CPU utilization: 1.00 CPUs   	[100.00%]

Reading: https://github.com/andikleen/pmu-tools/wiki/toplev-manual
Helped me understand most of above.

My specific CPU (i7-4790K @ 4.00GHz) unfortunately seems to have
limited "Frontend" support. E.g. 

 # perf record -g -a -e stalled-cycles-frontend
 Error:
 The stalled-cycles-frontend event is not supported.

And AFAIK icache misses are part of "frontend".


> Unfortunately the perf command it gives me fails with:
>  "invalid or unsupported event".
> 
> Perf command:
> 
>  sudo ./ocperf.py record -g -e \
  cpu/event=0xc5,umask=0x0,name=Branch_Resteers_BR_MISP_RETIRED_ALL_BRANCHES:pp,period=400009/pp,\
  cpu/event=0xd,umask=0x3,cmask=1,name=Bad_Speculation_INT_MISC_RECOVERY_CYCLES,period=2000003/,\
  cpu/event=0xd1,umask=0x1,name=L1_Bound_MEM_LOAD_UOPS_RETIRED_L1_HIT:pp,period=2000003/pp,\
  cpu/event=0xd1,umask=0x40,name=L1_Bound_MEM_LOAD_UOPS_RETIRED_HIT_LFB:pp,period=100003/pp \
  -C 0,4 -a

I fixed the problem with this perf command by removing the ":pp" part.
Perhaps your tool need to fix that?

A working command line looks like this:

 sudo ./ocperf.py record -g -e \
cpu/event=0xc5,umask=0x0,name=Branch_Resteers_BR_MISP_RETIRED_ALL_BRANCHES,period=400009/pp,\
cpu/event=0xd,umask=0x3,cmask=1,name=Bad_Speculation_INT_MISC_RECOVERY_CYCLES,period=2000003/,\
cpu/event=0xd1,umask=0x1,name=L1_Bound_MEM_LOAD_UOPS_RETIRED_L1_HIT,period=2000003/pp,\
cpu/event=0xd1,umask=0x40,name=L1_Bound_MEM_LOAD_UOPS_RETIRED_HIT_LFB,period=100003/pp \
  -C 0,4 -a

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer
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