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| author | Jens Axboe <jens.axboe@oracle.com> | 2009-04-14 16:18:16 +0400 |
|---|---|---|
| committer | Jens Axboe <jens.axboe@oracle.com> | 2009-04-15 10:28:12 +0400 |
| commit | d6ceb25e8d8bccf826848c2621a50d02c0a7f4ae (patch) | |
| tree | 31dec01cb624b27a1c29a5886dd801a67bba525e | |
| parent | 053c525fcf976810f023d96472f414c0d5e6339b (diff) | |
| download | linux-d6ceb25e8d8bccf826848c2621a50d02c0a7f4ae.tar.xz | |
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>
| -rw-r--r-- | block/cfq-iosched.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index cba8a5d91bfa..56e9d8503cf1 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1903,10 +1903,17 @@ cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq, * Remember that we saw a request from this process, but * don't start queuing just yet. Otherwise we risk seeing lots * of tiny requests, because we disrupt the normal plugging - * and merging. + * and merging. If the request is already larger than a single + * page, let it rip immediately. For that case we assume that + * merging is already done. */ - if (cfq_cfqq_wait_request(cfqq)) + if (cfq_cfqq_wait_request(cfqq)) { + if (blk_rq_bytes(rq) > PAGE_CACHE_SIZE) { + del_timer(&cfqd->idle_slice_timer); + blk_start_queueing(cfqd->queue); + } cfq_mark_cfqq_must_dispatch(cfqq); + } } else if (cfq_should_preempt(cfqd, cfqq, rq)) { /* * not the active queue - expire current slice if it is |