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Subject[PATCH 2/2] cfq: allow dispatching of both sync and async I/O together
Date
Hi,

In testing a workload that has a single fsync-ing process and another
process that does a sequential buffered read, I was unable to tune CFQ
to reach the throughput of deadline. This patch, along with the previous
one, brought CFQ in line with deadline when setting slice_idle to 0.

I'm not sure what the original reason for not allowing sync and async
I/O to be dispatched together was. If there is a workload I should be
testing that shows the inherent problems of this, please point me at it
and I will resume testing. Until and unless that workload is identified,
please consider applying this patch.

Cheers,
Jeff

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
---
block/cfq-iosched.c | 12 ------------
1 files changed, 0 insertions(+), 12 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 572a050..dab836e 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2296,18 +2296,6 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
{
unsigned int max_dispatch;

- /*
- * Drain async requests before we start sync IO
- */
- if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_flight[BLK_RW_ASYNC])
- return false;
-
- /*
- * If this is an async queue and we have sync IO in flight, let it wait
- */
- if (cfqd->rq_in_flight[BLK_RW_SYNC] && !cfq_cfqq_sync(cfqq))
- return false;
-
max_dispatch = max_t(unsigned int, cfqd->cfq_quantum / 2, 1);
if (cfq_class_idle(cfqq))
max_dispatch = 1;
--
1.6.5.2


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