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From: Christoph Hellwig <hch@lst.de>
To: Dave Chinner <david@fromorbit.com>
Cc: rpeterso@redhat.com, linux-fsdevel@vger.kernel.org, xfs@oss.sgi.com
Subject: Re: iomap infrastructure and multipage writes V2
Date: Mon, 2 May 2016 20:23:41 +0200	[thread overview]
Message-ID: <20160502182341.GA7077@lst.de> (raw)
In-Reply-To: <20160413215442.GS567@dastard>

Hi Dave,

sorry for taking forever to get back to this - travel to LSF and some
other meetings and a dealine last week didn't leave me any time for
XFS work.

On Thu, Apr 14, 2016 at 07:54:42AM +1000, Dave Chinner wrote:
> Christoph, have you done any perf testing of this patchset yet to
> check that it does indeed reduce the CPU overhead of large write
> operations? I'd also be interested to know if there is any change in
> overhead for single page (4k) IOs as well, even though I suspect
> there won't be.

I've done a lot of testing earlier, and this version also looks very
promising.  On the sort of hardware I have access to now, the 4k
numbers don't change much, but with 1M writes we both increase the
write bandwith a little bit and significantly lower the cpu usage.

The simple test that demonstrates this is this, the runs are from
a 4p VM with 4G of RAM, access to a fast NVMe SSD and a small enough
data size so that writeback shouldn't throttle the buffered write
path:

MNT=/mnt
PERF="perf_3.16"        # soo smart to have tools in the kernel tree..

#BS=4k
#COUNT=65536
BS=1M
COUNT=256

$PERF stat dd if=/dev/zero of=$MNT/testfile bs=$BS count=$COUNT

with the baseline for-next tree I get the following bandwith and
cpu utilization:

BS=4k: ~600MB/s			0.856 CPUs utilized ( +-  0.32% )
BS=1M: 1.45GB/s			0.820 CPUs utilized ( +-  0.77% )

with all patches applied:

BS=4k:	~610MB/s		0.848 CPUs utilized ( +-  0.36% )
BS=1M:	~1.55GB/s		0.615 CPUs utilized ( +-  0.80% )

This is also visible in the walltime

baseline, 4k:

real	0m0.540s
user	0m0.000s
sys	0m0.533s

baseline, 1M:

real	0m0.310s
user	0m0.000s
sys	0m0.313s

multipage, 4k:

real	0m0.541s
user	0m0.010s
sys	0m0.527s

multipage, 1M:

real	0m0.272s
user	0m0.000s
sys	0m0.263s

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      reply	other threads:[~2016-05-02 18:23 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-12 20:52 iomap infrastructure and multipage writes V2 Christoph Hellwig
2016-04-12 20:52 ` [PATCH 1/8] fs: move struct iomap from exportfs.h to a separate header Christoph Hellwig
2016-04-12 20:52 ` [PATCH 2/8] fs: introduce iomap infrastructure Christoph Hellwig
2016-04-12 20:52 ` [PATCH 3/8] xfs: make xfs_bmbt_to_iomap available outside of xfs_pnfs.c Christoph Hellwig
2016-04-12 20:52 ` [PATCH 4/8] xfs: reorder zeroing and flushing sequence in truncate Christoph Hellwig
2016-04-12 20:52 ` [PATCH 5/8] xfs: implement iomap based buffered write path Christoph Hellwig
2016-04-14 12:58   ` Brian Foster
2016-05-02 18:25     ` Christoph Hellwig
2016-05-03 15:02       ` Brian Foster
2016-05-03 18:15         ` Christoph Hellwig
2016-04-12 20:53 ` [PATCH 6/8] xfs: remove buffered write support from __xfs_get_blocks Christoph Hellwig
2016-04-12 20:53 ` [PATCH 7/8] fs: iomap based fiemap implementation Christoph Hellwig
2016-04-12 20:53 ` [PATCH 8/8] xfs: use iomap " Christoph Hellwig
2016-04-13 21:54 ` iomap infrastructure and multipage writes V2 Dave Chinner
2016-05-02 18:23   ` Christoph Hellwig [this message]

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