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Date: Sun, 29 Jan 2012 11:03:00 +0100 From: Eric Dumazet <eric.dumazet@...il.com> To: Wu Fengguang <wfg@...ux.intel.com> Cc: Herbert Poetzl <herbert@...hfloor.at>, Andrew Morton <akpm@...ux-foundation.org>, LKML <linux-kernel@...r.kernel.org>, Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org> Subject: Re: Bad SSD performance with recent kernels 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@...bao.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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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