Messages in this thread | | | Subject | Re: Large write = large latency for small writes | From | Peter Zijlstra <> | Date | Tue, 17 Mar 2009 23:09:12 +0100 |
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On Tue, 2009-03-17 at 13:19 -0700, David Rees wrote:
> I have a simple test case which demonstrates the huge increase in > write latency that occurs for small writes when a large disk > saturating write is also in progress [3]: > > dd if=/dev/zero of=/tmp/bigfile bs=1M count=10000 conv=fdatasync & > sleep 10 > time dd if=/dev/zero of=/tmp/smallfile bs=4k count=1 conv=fdatasync > > On a handful of systems I have access to, it took anywhere from 6-45 > seconds for the small write to complete. Others in the bug have > reproduced this across a number of filesystems (ext3, reiserfs, ext4). > xfs in particular seems to handle this test case better than the > others. As do systems which can sustain high write speeds.
How does it fare without the fdatasync?
That is, is it the sync that's taking ages, or the ditry?
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