From: Shaohua Li Date: Fri, 8 Jul 2011 06:19:20 +0000 (+0200) Subject: block: avoid building too big plug list X-Git-Tag: v3.1-rc1~252^2~10 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=55c022bbddb2c056b5dff1bd1b1758d31b6d64c9;p=pandora-kernel.git block: avoid building too big plug list When I test fio script with big I/O depth, I found the total throughput drops compared to some relative small I/O depth. The reason is the thread accumulates big requests in its plug list and causes some delays (surely this depends on CPU speed). I thought we'd better have a threshold for requests. When a threshold reaches, this means there is no request merge and queue lock contention isn't severe when pushing per-task requests to queue, so the main advantages of blk plug don't exist. We can force a plug list flush in this case. With this, my test throughput actually increases and almost equals to small I/O depth. Another side effect is irq off time decreases in blk_flush_plug_list() for big I/O depth. The BLK_MAX_REQUEST_COUNT is choosen arbitarily, but 16 is efficiently to reduce lock contention to me. But I'm open here, 32 is ok in my test too. Signed-off-by: Shaohua Li Signed-off-by: Jens Axboe --- Reading git-diff-tree failed