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authorShaohua Li <shaohua.li@intel.com>2011-07-08 02:19:20 -0400
committerJens Axboe <jaxboe@fusionio.com>2011-07-08 02:19:20 -0400
commit55c022bbddb2c056b5dff1bd1b1758d31b6d64c9 (patch)
treefdd3aa29a1407bbd19b8efe47b2538544da85a70 /kernel
parent719c0c590609809365c6f3da2f923cd84dc99113 (diff)
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 <shaohua.li@intel.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
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