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Message-ID: <20110918143721.GA17240@localhost>
Date: Sun, 18 Sep 2011 22:37:21 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
Dave Chinner <david@...morbit.com>,
Greg Thelen <gthelen@...gle.com>,
Minchan Kim <minchan.kim@...il.com>,
Vivek Goyal <vgoyal@...hat.com>,
Andrea Righi <arighi@...eler.com>,
linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/18] writeback: dirty position control - bdi reserve
area
On Sun, Sep 18, 2011 at 10:17:05PM +0800, Wu Fengguang wrote:
> On Mon, Sep 12, 2011 at 06:19:38PM +0800, Peter Zijlstra wrote:
> > On Wed, 2011-09-07 at 20:31 +0800, Wu Fengguang wrote:
> > > > > + x_intercept = min(write_bw, freerun);
> > > > > + if (bdi_dirty < x_intercept) {
> > > >
> > > > So the point of the freerun point is that we never throttle before it,
> > > > so basically all the below shouldn't be needed at all, right?
> > >
> > > Yes!
> > >
> > > > > + if (bdi_dirty > x_intercept / 8) {
> > > > > + pos_ratio *= x_intercept;
> > > > > + do_div(pos_ratio, bdi_dirty);
> > > > > + } else
> > > > > + pos_ratio *= 8;
> > > > > + }
> > > > > +
> > > > > return pos_ratio;
> > > > > }
> >
> > Does that mean we can remove this whole block?
>
> Right, if the bdi freerun concept is proved to work fine.
>
> Unfortunately I find it mostly yields lower performance than bdi
> reserve area. Patch is attached. If you would like me try other
> patches, I can easily kick off new tests and redo the comparison.
>
> Here is the nr_written numbers over various JBOD test cases,
> the larger, the better:
>
> bdi-reserve bdi-freerun diff case
> ---------------------------------------------------------------------------------------
> 38375271 31553807 -17.8% JBOD-10HDD-6G/xfs-100dd-1M-16p-5895M-20
> 30478879 28631491 -6.1% JBOD-10HDD-6G/xfs-10dd-1M-16p-5895M-20
> 29735407 28871956 -2.9% JBOD-10HDD-6G/xfs-1dd-1M-16p-5895M-20
> 30850350 28344165 -8.1% JBOD-10HDD-6G/xfs-2dd-1M-16p-5895M-20
> 17706200 16174684 -8.6% JBOD-10HDD-thresh=100M/xfs-100dd-1M-16p-5895M-100M
> 23374918 14376942 -38.5% JBOD-10HDD-thresh=100M/xfs-10dd-1M-16p-5895M-100M
> 20659278 19640375 -4.9% JBOD-10HDD-thresh=100M/xfs-1dd-1M-16p-5895M-100M
> 22517497 14552321 -35.4% JBOD-10HDD-thresh=100M/xfs-2dd-1M-16p-5895M-100M
> 68287850 61078553 -10.6% JBOD-10HDD-thresh=2G/xfs-100dd-1M-16p-5895M-2048M
> 33835247 32018425 -5.4% JBOD-10HDD-thresh=2G/xfs-10dd-1M-16p-5895M-2048M
> 30187817 29942083 -0.8% JBOD-10HDD-thresh=2G/xfs-1dd-1M-16p-5895M-2048M
> 30563144 30204022 -1.2% JBOD-10HDD-thresh=2G/xfs-2dd-1M-16p-5895M-2048M
> 34476862 34645398 +0.5% JBOD-10HDD-thresh=4G/xfs-10dd-1M-16p-5895M-4096M
> 30326479 30097263 -0.8% JBOD-10HDD-thresh=4G/xfs-1dd-1M-16p-5895M-4096M
> 30446767 30339683 -0.4% JBOD-10HDD-thresh=4G/xfs-2dd-1M-16p-5895M-4096M
> 40793956 45936678 +12.6% JBOD-10HDD-thresh=800M/xfs-100dd-1M-16p-5895M-800M
> 27481305 24867282 -9.5% JBOD-10HDD-thresh=800M/xfs-10dd-1M-16p-5895M-800M
> 25651257 22507406 -12.3% JBOD-10HDD-thresh=800M/xfs-1dd-1M-16p-5895M-800M
> 19849350 21298787 +7.3% JBOD-10HDD-thresh=800M/xfs-2dd-1M-16p-5895M-800M
BTW, I also compared the IO-less patchset and the vanilla kernel's
JBOD performance. Basically, the performance is lightly improved
under large memory, and reduced a lot in small memory servers.
vanillla IO-less
--------------------------------------------------------------------------------
31189025 34476862 +10.5% JBOD-10HDD-thresh=4G/xfs-10dd-1M-16p-5895M-4096M
30441974 30326479 -0.4% JBOD-10HDD-thresh=4G/xfs-1dd-1M-16p-5895M-4096M
30484578 30446767 -0.1% JBOD-10HDD-thresh=4G/xfs-2dd-1M-16p-5895M-4096M
68532421 68287850 -0.4% JBOD-10HDD-thresh=2G/xfs-100dd-1M-16p-5895M-2048M
31606793 33835247 +7.1% JBOD-10HDD-thresh=2G/xfs-10dd-1M-16p-5895M-2048M
30404955 30187817 -0.7% JBOD-10HDD-thresh=2G/xfs-1dd-1M-16p-5895M-2048M
30425591 30563144 +0.5% JBOD-10HDD-thresh=2G/xfs-2dd-1M-16p-5895M-2048M
40451069 38375271 -5.1% JBOD-10HDD-6G/xfs-100dd-1M-16p-5895M-20
30903629 30478879 -1.4% JBOD-10HDD-6G/xfs-10dd-1M-16p-5895M-20
30113560 29735407 -1.3% JBOD-10HDD-6G/xfs-1dd-1M-16p-5895M-20
30181418 30850350 +2.2% JBOD-10HDD-6G/xfs-2dd-1M-16p-5895M-20
46067335 40793956 -11.4% JBOD-10HDD-thresh=800M/xfs-100dd-1M-16p-5895M-800M
30425063 27481305 -9.7% JBOD-10HDD-thresh=800M/xfs-10dd-1M-16p-5895M-800M
28437929 25651257 -9.8% JBOD-10HDD-thresh=800M/xfs-1dd-1M-16p-5895M-800M
29409406 19849350 -32.5% JBOD-10HDD-thresh=800M/xfs-2dd-1M-16p-5895M-800M
26508063 17706200 -33.2% JBOD-10HDD-thresh=100M/xfs-100dd-1M-16p-5895M-100M
23767810 23374918 -1.7% JBOD-10HDD-thresh=100M/xfs-10dd-1M-16p-5895M-100M
28032891 20659278 -26.3% JBOD-10HDD-thresh=100M/xfs-1dd-1M-16p-5895M-100M
26049973 22517497 -13.6% JBOD-10HDD-thresh=100M/xfs-2dd-1M-16p-5895M-100M
There are still some itches in JBOD..
Thanks,
Fengguang
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