linux-kernel - Re: zram: per-cpu compression streams

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Date:	Fri, 25 Mar 2016 10:47:06 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: zram: per-cpu compression streams

Hello Minchan,

On (03/25/16 08:41), Minchan Kim wrote:
[..]
> >  Test #10 iozone -t 10 -R -r 80K -s 0M -I +Z
> >    Initial write        3213973.56      2731512.62      4416466.25*
> >          Rewrite        3066956.44*     2693819.50       332671.94
> >             Read        7769523.25*     2681473.75       462840.44
> >          Re-read        5244861.75      5473037.00*      382183.03
> >     Reverse Read        7479397.25*     4869597.75       374714.06
> >      Stride read        5403282.50*     5385083.75       382473.44
> >      Random read        5131997.25      5176799.75*      380593.56
> >   Mixed workload        3998043.25      4219049.00*     1645850.45
> >     Random write        3452832.88      3290861.69      3588531.75*
> >           Pwrite        3757435.81      2711756.47      4561807.88*
> >            Pread        2743595.25*     2635835.00       412947.98
> >           Fwrite       16076549.00     16741977.25*    14797209.38
> >            Fread       23581812.62*    21664184.25      5064296.97
> >  =          real         0m44.490s       0m44.444s       0m44.609s
> >  =          user          0m0.054s        0m0.049s        0m0.055s
> >  =           sys          0m0.037s        0m0.046s        0m0.148s
> >  
> >  
> >  so when the number of active tasks become larger than the number
> >  of online CPUS, iozone reports a bit hard to understand data. I
> >  can assume that since now we keep the preemption disabled longer
> >  in write path, a concurrent operation (READ or WRITE) cannot preempt
> >  current anymore... slightly suspicious.
> >  
> >  the other hard to understand thing is why do READ-only tests have
> >  such a huge jitter. READ-only tests don't depend on streams, they
> >  don't even use them, we supply compressed data directly to
> >  decompression api.
> >  
> >  may be better retire iozone and never use it again.
> >  
> >  
> >  "118 insertions(+), 238 deletions(-)" the patches remove a big
> >  pile of code.
> 
> First of all, I appreciate you very much!

thanks!

> At a glance, on write workload, huge win but worth to investigate
> how such fluctuation/regression happens on read-related test
> (read and mixed workload).

yes, was going to investigate in more details but got interrupted,
will return back to it today/tomorrow.

> Could you send your patchset? I will test it.

oh, sorry, sure! attached (because it's not a real patch submission
yet, but they look more or less ready I guess).

patches are against next-20160324.

	-ss

View attachment "0001-zsmalloc-require-GFP-in-zs_malloc.patch" of type "text/x-diff" (3948 bytes)

View attachment "0002-zram-switch-to-per-cpu-streams.patch" of type "text/x-diff" (13135 bytes)