2010-12-14 06:32:11

by Gui, Jianfeng/归 剑峰

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

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 <[email protected]>
---
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

2010-12-14 16:56:38

by Jeff Moyer

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

Gui Jianfeng <[email protected]> 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 <[email protected]>

2010-12-14 22:25:27

by Vivek Goyal

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

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 <[email protected]>
> ---

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

Acked-by: Vivek Goyal <[email protected]>

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
>