[PATCH] CFQ: mark must_alloc flag when a cfqq doesn't allocate any request

[PATCH] CFQ: mark must_alloc flag when a cfqq doesn't allocate any request

[Gui Jianfeng]

Hi Jens,

CFQ judges whether must_alloc flag is set, but never marks this flag.
This patch set must_alloc flag when there is no request allocated by
a cfqq. This change ensures cfqq will get at least one request even
if the queue is full.
Hope it helps.

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
---
 block/cfq-iosched.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index fd7080e..531a404 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2279,6 +2279,9 @@ static void cfq_put_request(struct request *rq)
 		BUG_ON(!cfqq->allocated[rw]);
 		cfqq->allocated[rw]--;
 
+		if (!(cfqq->allocated[0] + cfqq->allocated[1]))
+			cfq_mark_cfqq_must_alloc(cfqq);
+
 		put_io_context(RQ_CIC(rq)->ioc);
 
 		rq->elevator_private = NULL;
-- 
1.5.4.rc3

Re: [PATCH] CFQ: mark must_alloc flag when a cfqq doesn't allocate any request

[Jens Axboe]

On Fri, Aug 07 2009, Gui Jianfeng wrote:
> Hi Jens,
> 
> CFQ judges whether must_alloc flag is set, but never marks this flag.
> This patch set must_alloc flag when there is no request allocated by
> a cfqq. This change ensures cfqq will get at least one request even
> if the queue is full.
> Hope it helps.

The flag became redundant with the fix to not fail in set_request(). I
don't think your below patch is a very good idea, it would basically
mark any queue that has previously had a request allocated as a must
alloc queue. It would make more sense to mark an idling queue as must
alloc, since it's critical that this queue is allowed to allocate a
request once we idle a queue on its behalf. But we already check for the
wait_request flag in ->may_queue, so that part is already covered. So
I'd suggest we just delete any reference to must_alloc instead.


> 
> Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
> ---
>  block/cfq-iosched.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index fd7080e..531a404 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -2279,6 +2279,9 @@ static void cfq_put_request(struct request *rq)
>  		BUG_ON(!cfqq->allocated[rw]);
>  		cfqq->allocated[rw]--;
>  
> +		if (!(cfqq->allocated[0] + cfqq->allocated[1]))
> +			cfq_mark_cfqq_must_alloc(cfqq);
> +
>  		put_io_context(RQ_CIC(rq)->ioc);
>  
>  		rq->elevator_private = NULL;
> -- 
> 1.5.4.rc3
> 
> 

-- 
Jens Axboe

[PATCH] CFQ: get rid of must_alloc flag

[Gui Jianfeng]

Get rid of must_alloc flag since it's redundant now.

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
---
 block/cfq-iosched.c |    6 +-----
 1 files changed, 1 insertions(+), 5 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index fd7080e..f5770ad 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -191,7 +191,6 @@ enum cfqq_state_flags {
 	CFQ_CFQQ_FLAG_on_rr = 0,	/* on round-robin busy list */
 	CFQ_CFQQ_FLAG_wait_request,	/* waiting for a request */
 	CFQ_CFQQ_FLAG_must_dispatch,	/* must be allowed a dispatch */
-	CFQ_CFQQ_FLAG_must_alloc,	/* must be allowed rq alloc */
 	CFQ_CFQQ_FLAG_must_alloc_slice,	/* per-slice must_alloc flag */
 	CFQ_CFQQ_FLAG_fifo_expire,	/* FIFO checked in this slice */
 	CFQ_CFQQ_FLAG_idle_window,	/* slice idling enabled */
@@ -218,7 +217,6 @@ static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq)		\
 CFQ_CFQQ_FNS(on_rr);
 CFQ_CFQQ_FNS(wait_request);
 CFQ_CFQQ_FNS(must_dispatch);
-CFQ_CFQQ_FNS(must_alloc);
 CFQ_CFQQ_FNS(must_alloc_slice);
 CFQ_CFQQ_FNS(fifo_expire);
 CFQ_CFQQ_FNS(idle_window);
@@ -2229,8 +2227,7 @@ static void cfq_prio_boost(struct cfq_queue *cfqq)
 
 static inline int __cfq_may_queue(struct cfq_queue *cfqq)
 {
-	if ((cfq_cfqq_wait_request(cfqq) || cfq_cfqq_must_alloc(cfqq)) &&
-	    !cfq_cfqq_must_alloc_slice(cfqq)) {
+	if ((cfq_cfqq_wait_request(cfqq) && !cfq_cfqq_must_alloc_slice(cfqq)) {
 		cfq_mark_cfqq_must_alloc_slice(cfqq);
 		return ELV_MQUEUE_MUST;
 	}
@@ -2317,7 +2314,6 @@ cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
 	}
 
 	cfqq->allocated[rw]++;
-	cfq_clear_cfqq_must_alloc(cfqq);
 	atomic_inc(&cfqq->ref);
 
 	spin_unlock_irqrestore(q->queue_lock, flags);
-- 
1.5.4.rc3

Re: [PATCH] CFQ: get rid of must_alloc flag

[Jens Axboe]

On Tue, Aug 18 2009, Gui Jianfeng wrote:
> Get rid of must_alloc flag since it's redundant now.

I already queued an identical patch in for-2.6.32 a week ago:

http://git.kernel.dk/?p=linux-2.6-block.git;a=commitdiff;h=87783e4b0213b6b000108f17e2cd91045bee56f7;hp=37571a15498816c1a35f1dd2b68f7ddac5c50592

-- 
Jens Axboe

Re: [PATCH] CFQ: get rid of must_alloc flag

[Gui Jianfeng]

Jens Axboe wrote:
> On Tue, Aug 18 2009, Gui Jianfeng wrote:
>> Get rid of must_alloc flag since it's redundant now.
> 
> I already queued an identical patch in for-2.6.32 a week ago:
> 
> http://git.kernel.dk/?p=linux-2.6-block.git;a=commitdiff;h=87783e4b0213b6b000108f17e2cd91045bee56f7;hp=37571a15498816c1a35f1dd2b68f7ddac5c50592
> 

Ahh.. see, sorry for bothering.

-- 
Regards
Gui Jianfeng

Re: [PATCH] CFQ: get rid of must_alloc flag

[Jens Axboe]

On Tue, Aug 18 2009, Gui Jianfeng wrote:
> Jens Axboe wrote:
> > On Tue, Aug 18 2009, Gui Jianfeng wrote:
> >> Get rid of must_alloc flag since it's redundant now.
> > 
> > I already queued an identical patch in for-2.6.32 a week ago:
> > 
> > http://git.kernel.dk/?p=linux-2.6-block.git;a=commitdiff;h=87783e4b0213b6b000108f17e2cd91045bee56f7;hp=37571a15498816c1a35f1dd2b68f7ddac5c50592
> > 
> 
> Ahh.. see, sorry for bothering.

Don't apologize, thanks for noticing!

-- 
Jens Axboe