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authorJens Axboe <jens.axboe@oracle.com>2009-04-14 14:18:16 +0200
committerJens Axboe <jens.axboe@oracle.com>2009-04-15 08:28:12 +0200
commitd6ceb25e8d8bccf826848c2621a50d02c0a7f4ae (patch)
tree31dec01cb624b27a1c29a5886dd801a67bba525e /REPORTING-BUGS
parent053c525fcf976810f023d96472f414c0d5e6339b (diff)
cfq-iosched: don't delay queue kick for a merged request
"Zhang, Yanmin" <yanmin_zhang@linux.intel.com> reports that commit b029195dda0129b427c6e579a3bb3ae752da3a93 introduced a regression of about 50% with sequential threaded read workloads. The test case is: tiotest -k0 -k1 -k3 -f 80 -t 32 which starts 32 threads each reading a 80MB file. Twiddle the kick queue logic so that we do start IO immediately, if it appears to be a fully merged request. We can't really detect that, so just check if the request is bigger than a page or not. The assumption is that since single bio issues will first queue a single request with just one page attached and then later do merges on that, if we already have more than a page worth of data in the request, then the request is most likely good to go. Verified that this doesn't cause a regression with the test case that commit b029195dda0129b427c6e579a3bb3ae752da3a93 was fixing. It does not, we still see maximum sized requests for the queue-then-merge cases. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
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