Messages in this thread | | | Subject | Re: Bad SSD performance with recent kernels | From | Eric Dumazet <> | Date | Sun, 29 Jan 2012 11:03:00 +0100 |
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Le dimanche 29 janvier 2012 à 13:59 +0800, Wu Fengguang a écrit :
> What's the block size? If it's < 4k, performance might be hurt. > > blockdev --getbsz /dev/sda >
# blockdev --getbsz /dev/sda 4096
> > FYI, I started a bisection. > > Thank you! If the bisection would take much human time, it should be > easier to collect some blktrace data on reading /dev/sda for analyzes. >
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.
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
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