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authorJens Axboe <jaxboe@fusionio.com>2011-05-17 11:04:44 +0200
committerJens Axboe <jaxboe@fusionio.com>2011-05-17 11:04:44 +0200
commit9937a5e2f32892db0dbeefc2b3bc74b3ae3ea9c7 (patch)
tree0448e96b503deb71dd8a1228da94a9fc22a57d48 /block
parent70087dc38cc77ca8f46059564c00338777734762 (diff)
scsi: remove performance regression due to async queue run
Commit c21e6beb removed our queue request_fn re-enter protection, and defaulted to always running the queues from kblockd to be safe. This was a known potential slow down, but should be safe. Unfortunately this is causing big performance regressions for some, so we need to improve this logic. Looking into the details of the re-enter, the real issue is on requeue of requests. Requeue of requests upon seeing a BUSY condition from the device ends up re-running the queue, causing traces like this: scsi_request_fn() scsi_dispatch_cmd() scsi_queue_insert() __scsi_queue_insert() scsi_run_queue() scsi_request_fn() ... potentially causing the issue we want to avoid. So special case the requeue re-run of the queue, but improve it to offload the entire run of local queue and starved queue from a single workqueue callback. This is a lot better than potentially kicking off a workqueue run for each device seen. This also fixes the issue of the local device going into recursion, since the above mentioned commit never moved that queue run out of line. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
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