linux-kernel - Re: performance regression due to commit e82e0561("mm: vmscan: obey proportional scanning requirements for kswapd")

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Date:	Tue, 18 Mar 2014 20:20:15 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Yuanhan Liu <yuanhan.liu@...ux.intel.com>
cc:	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Suleiman Souhlal <suleiman@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: performance regression due to commit e82e0561("mm: vmscan: obey
 proportional scanning requirements for kswapd")

On Tue, 18 Mar 2014, Yuanhan Liu wrote:
> On Sat, Mar 15, 2014 at 08:56:10PM -0700, Hugh Dickins wrote:
> > On Fri, 14 Mar 2014, Mel Gorman wrote:
> > > 
> > > You say it's already been tested for months but it would be nice if the
> > > workload that generated this thread was also tested.
> > 
> > Yes indeed: Yuanhan, do you have time to try this patch for your
> > testcase?  I'm hoping it will prove at least as effective as your
> > own suggested patch, but please let us know what you find - thanks.
> 
> Hi Hugh,
> 
> Sure, and sorry to tell you that this patch introduced another half
> performance descrease from avg 60 MB/s to 30 MB/s in this testcase.

Thanks a lot for trying it out.  I had been hoping that everything
would be wonderful, and I wouldn't have think at all about what's
going on.  You have made me sad :( but I can't blame your honesty!

I'll have to think a little after all, about your test, and Mel's
pertinent questions: I'll come back to you, nothing to say right now.

Hugh

> 
> Moreover, the dd throughput for each process was steady before, however,
> it's quite bumpy from 20 MB/s to 40 MB/s w/ this patch applied, and thus
> got a avg of 30 MB/s:
> 
>     11327188992 bytes (11 GB) copied, 300.014 s, 37.8 MB/s
>     1809373+0 records in
>     1809372+0 records out
>     7411187712 bytes (7.4 GB) copied, 300.008 s, 24.7 MB/s
>     3068285+0 records in
>     3068284+0 records out
>     12567691264 bytes (13 GB) copied, 300.001 s, 41.9 MB/s
>     1883877+0 records in
>     1883876+0 records out
>     7716356096 bytes (7.7 GB) copied, 300.002 s, 25.7 MB/s
>     1807674+0 records in
>     1807673+0 records out
>     7404228608 bytes (7.4 GB) copied, 300.024 s, 24.7 MB/s
>     1796473+0 records in
>     1796472+0 records out
>     7358349312 bytes (7.4 GB) copied, 300.008 s, 24.5 MB/s
>     1905655+0 records in
>     1905654+0 records out
>     7805558784 bytes (7.8 GB) copied, 300.016 s, 26.0 MB/s
>     2819168+0 records in
>     2819167+0 records out
>     11547308032 bytes (12 GB) copied, 300.025 s, 38.5 MB/s
>     1848381+0 records in
>     1848380+0 records out
>     7570964480 bytes (7.6 GB) copied, 300.005 s, 25.2 MB/s
>     3023133+0 records in
>     3023132+0 records out
>     12382748672 bytes (12 GB) copied, 300.024 s, 41.3 MB/s
>     1714585+0 records in
>     1714584+0 records out
>     7022936064 bytes (7.0 GB) copied, 300.011 s, 23.4 MB/s
>     1835132+0 records in
>     1835131+0 records out
>     7516696576 bytes (7.5 GB) copied, 299.998 s, 25.1 MB/s
>     1733341+0 records in
>     
> 
> 	--yliu
> 
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