block: change force plug flush call order
Do blk_flush_plug_list() first and then add new request aDo blk_flush_plug_list() first and then add new request aDo blk_flush_plug_list() first and then add new request at the tail. New request can't be merged to existing requests, but later new requests might be merged with this new one. If blk_flush_plug_list() is done later, the merge doesn't happen. Believe it or not, this fixes a 10% regression running sysbench workload. Signed-off-by: Shaohua Li <shli@kernel.org> Signed-off-by: Shaohua Li <shaohua.li@intel.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
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e8037d4983
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a632716275
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@ -1302,11 +1302,11 @@ get_rq:
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if (__rq->q != q)
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plug->should_sort = 1;
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}
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list_add_tail(&req->queuelist, &plug->list);
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plug->count++;
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drive_stat_acct(req, 1);
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if (plug->count >= BLK_MAX_REQUEST_COUNT)
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blk_flush_plug_list(plug, false);
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plug->count++;
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list_add_tail(&req->queuelist, &plug->list);
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drive_stat_acct(req, 1);
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} else {
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spin_lock_irq(q->queue_lock);
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add_acct_request(q, req, where);
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