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authorJens Axboe <jens.axboe@oracle.com>2009-04-07 08:51:19 +0200
committerJens Axboe <jens.axboe@oracle.com>2009-04-07 08:51:19 +0200
commit2f5cb7381b737e24c8046fd4aeab571fb71315f5 (patch)
tree27b82d748bdf99296b8a914c51dad2fbea90aea3 /init
parent3fbed4c61abd8458896e38633d10110cb5a589d4 (diff)
cfq-iosched: change dispatch logic to deal with single requests at the time
The IO scheduler core calls into the IO scheduler dispatch_request hook to move requests from the IO scheduler and into the driver dispatch list. It only does so when the dispatch list is empty. CFQ moves several requests to the dispatch list, which can cause higher latencies if we suddenly have to switch to some important sync IO. Change the logic to move one request at the time instead. This should almost be functionally equivalent to what we did before, except that we now honor 'quantum' as the maximum queue depth at the device side from any single cfqq. If there's just a single active cfqq, we allow up to 4 times the normal quantum. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
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