Messages in this thread | | | Date | Mon, 30 Jan 2012 22:48:21 +0800 | From | Wu Fengguang <> | Subject | Re: Bad SSD performance with recent kernels |
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On Sun, Jan 29, 2012 at 11:03:00AM +0100, Eric Dumazet wrote:
> Very strange, my bissection ended on following commit : > > commit 805f6b5e1cbfedfb9b3d354013e7f4b13a79270f > Author: Tao Ma <boyu.mt@taobao.com> > Date: Fri Mar 11 20:11:59 2011 +0100 > > blktrace: Use rq->cmd_flags directly in blk_add_trace_rq. > > This makes no sense.
Yeah, commit 55602dd66f535 ("fs: make generic file read/write functions plug") looks like the real root cause and should probably be reverted as a whole. Buffered read/write syscalls are not directly tied to IO after all (readahead/writeback have the right plug points).
Thanks, Fengguang
> hdparm uses 2MB block reads, so read_ahead (128KB) is too small for best > perf > > # cat /sys/class/block/sda/queue/read_ahead_kb > 128 > > # dd if=/dev/sda of=/dev/null bs=128k > ^C > 63744+0 enregistrements lus > 63743+0 enregistrements écrits > 8354922496 octets (8,4 GB) copiés, 39,975 s, 209 MB/s > > # hdparm -t /dev/sda > > /dev/sda: > Timing buffered disk reads: 510 MB in 3.00 seconds = 169.75 MB/sec > > # uname -a > Linux edumazet-laptop 3.0.0-15-generic #26-Ubuntu SMP Fri Jan 20 > 17:23:00 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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