Revert "cfq: Remove special treatment for metadata rqs."
We have a kernel build regression since 3.1-rc1, which is about 10%
regression. The kernel source is in an ext3 filesystem.
Alex Shi bisect it to commit:
commit a07405b7802691d29ab3b23bdc76ee6d006aad0b
Author: Justin TerAvest <teravest@google.com>
Date: Sun Jul 10 22:09:19 2011 +0200
cfq: Remove special treatment for metadata rqs.
Apparently this is caused by lack metadata preemption, where ext3/ext4
do use READ_META. I didn't see a way to fix the issue, so suggest
reverting the patch.
This reverts commit a07405b7802691d29ab3b23bdc76ee6d006aad0b.
Reported-by: Alex Shi<alex.shi@intel.com>
Reported-by: Shaohua Li<shaohua.li@intel.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 6508345..a33bd43 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -130,6 +130,8 @@
unsigned long slice_end;
long slice_resid;
+ /* pending metadata requests */
+ int meta_pending;
/* number of requests that are on the dispatch list or inside driver */
int dispatched;
@@ -682,6 +684,9 @@
if (rq_is_sync(rq1) != rq_is_sync(rq2))
return rq_is_sync(rq1) ? rq1 : rq2;
+ if ((rq1->cmd_flags ^ rq2->cmd_flags) & REQ_META)
+ return rq1->cmd_flags & REQ_META ? rq1 : rq2;
+
s1 = blk_rq_pos(rq1);
s2 = blk_rq_pos(rq2);
@@ -1607,6 +1612,10 @@
cfqq->cfqd->rq_queued--;
cfq_blkiocg_update_io_remove_stats(&(RQ_CFQG(rq))->blkg,
rq_data_dir(rq), rq_is_sync(rq));
+ if (rq->cmd_flags & REQ_META) {
+ WARN_ON(!cfqq->meta_pending);
+ cfqq->meta_pending--;
+ }
}
static int cfq_merge(struct request_queue *q, struct request **req,
@@ -3360,6 +3369,13 @@
return true;
/*
+ * So both queues are sync. Let the new request get disk time if
+ * it's a metadata request and the current queue is doing regular IO.
+ */
+ if ((rq->cmd_flags & REQ_META) && !cfqq->meta_pending)
+ return true;
+
+ /*
* Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
*/
if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
@@ -3423,6 +3439,8 @@
struct cfq_io_context *cic = RQ_CIC(rq);
cfqd->rq_queued++;
+ if (rq->cmd_flags & REQ_META)
+ cfqq->meta_pending++;
cfq_update_io_thinktime(cfqd, cfqq, cic);
cfq_update_io_seektime(cfqd, cfqq, rq);
