2009-11-24 13:49:12

by Corrado Zoccolo

Subject: [PATCH 2/4] cfq-iosched: fix no-idle preemption logic

An incoming no-idle queue should preempt the active no-idle queue
only if the active queue is idling due to service tree empty.
Previous code was buggy in two ways:
* it relied on service_tree field to be set on the active queue, while
it is not set when the code is idling for a new request
* it didn't check for the service tree empty condition, so could lead to
LIFO behaviour if multiple queues with depth > 1 were preempting each
other on an non-NCQ device.

Reported-by: Vivek Goyal <[email protected]>
Signed-off-by: Corrado Zoccolo <[email protected]>
---
block/cfq-iosched.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 6925ab9..2a304f4 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2401,8 +2401,9 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
if (cfq_class_idle(cfqq))
return true;

- if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD
- && new_cfqq->service_tree == cfqq->service_tree)
+ if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD &&
+ cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD &&
+ new_cfqq->service_tree->count == 1)
return true;

/*
--
1.6.2.5

2009-11-24 14:37:06

by Vivek Goyal

Subject: Re: [PATCH 2/4] cfq-iosched: fix no-idle preemption logic

On Tue, Nov 24, 2009 at 02:49:02PM +0100, Corrado Zoccolo wrote:
> An incoming no-idle queue should preempt the active no-idle queue
> only if the active queue is idling due to service tree empty.
> Previous code was buggy in two ways:
> * it relied on service_tree field to be set on the active queue, while
> it is not set when the code is idling for a new request
> * it didn't check for the service tree empty condition, so could lead to
> LIFO behaviour if multiple queues with depth > 1 were preempting each
> other on an non-NCQ device.
>
> Reported-by: Vivek Goyal <[email protected]>
> Signed-off-by: Corrado Zoccolo <[email protected]>
> ---
> block/cfq-iosched.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index 6925ab9..2a304f4 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -2401,8 +2401,9 @@ cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
> if (cfq_class_idle(cfqq))
> return true;
>
> - if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD
> - && new_cfqq->service_tree == cfqq->service_tree)
> + if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD &&
> + cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD &&
> + new_cfqq->service_tree->count == 1)
> return true;
>

Looks good to me.

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

Thanks
Vivek