[PATCH] cfq-iosched: don't check cfqg in choose_service_tree()

[PATCH] cfq-iosched: don't check cfqg in choose_service_tree()

[Gui Jianfeng]

When cfq_choose_cfqg() is called in select_queue(), there must be at least one
backlogged CFQ queue waiting for dispatching, hence there must be at least one
backlogged CFQ group on service tree. So we never call choose_service_tree()
with cfqg == NULL.

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
---
 block/cfq-iosched.c |    6 ------
 1 files changed, 0 insertions(+), 6 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 9b186fd..c19d015 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2103,12 +2103,6 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
 	unsigned group_slice;
 	enum wl_prio_t original_prio = cfqd->serving_prio;
 
-	if (!cfqg) {
-		cfqd->serving_prio = IDLE_WORKLOAD;
-		cfqd->workload_expires = jiffies + 1;
-		return;
-	}
-
 	/* Choose next priority. RT > BE > IDLE */
 	if (cfq_group_busy_queues_wl(RT_WORKLOAD, cfqd, cfqg))
 		cfqd->serving_prio = RT_WORKLOAD;
-- 
1.6.5.2

Re: [PATCH] cfq-iosched: don't check cfqg in choose_service_tree()

[Jeff Moyer]

Gui Jianfeng <guijianfeng@cn.fujitsu.com> writes:

> When cfq_choose_cfqg() is called in select_queue(), there must be at least one
> backlogged CFQ queue waiting for dispatching, hence there must be at least one
> backlogged CFQ group on service tree. So we never call choose_service_tree()
> with cfqg == NULL.

Further, if cfqg was NULL, cfq_choose_cfqg would have dereferenced a
NULL pointer and we wouldn't even get to choose_service_tree.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

Re: [PATCH] cfq-iosched: don't check cfqg in choose_service_tree()

[Vivek Goyal]

On Tue, Dec 14, 2010 at 02:32:28PM +0800, Gui Jianfeng wrote:
> When cfq_choose_cfqg() is called in select_queue(), there must be at least one
> backlogged CFQ queue waiting for dispatching, hence there must be at least one
> backlogged CFQ group on service tree. So we never call choose_service_tree()
> with cfqg == NULL.
> 
> Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
> ---

Thanks Gui for the cleanup. This patch looks good to me.

Acked-by: Vivek Goyal <vgoyal@redhat.com>

Vivek

>  block/cfq-iosched.c |    6 ------
>  1 files changed, 0 insertions(+), 6 deletions(-)
> 
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 9b186fd..c19d015 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -2103,12 +2103,6 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
>  	unsigned group_slice;
>  	enum wl_prio_t original_prio = cfqd->serving_prio;
>  
> -	if (!cfqg) {
> -		cfqd->serving_prio = IDLE_WORKLOAD;
> -		cfqd->workload_expires = jiffies + 1;
> -		return;
> -	}
> -
>  	/* Choose next priority. RT > BE > IDLE */
>  	if (cfq_group_busy_queues_wl(RT_WORKLOAD, cfqd, cfqg))
>  		cfqd->serving_prio = RT_WORKLOAD;
> -- 
> 1.6.5.2
>