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items: [PATCH] cfq: wrong sync writes detection
items: Re: [PATCH] cfq: wrong sync writes detection

[PATCH] cfq: wrong sync writes detection
type: item
description: CFQ I/O scheduler does the following actions to find out whether the request is sync: rw = rq_data_dir(rq); => possible values for rw are 0 or 1 static inline pid_t cfq_queue_pid(struct task_struct *task, int rw) { if (rw == READ || rw == WRITE_SYNC) => second condition is always false return task->pid; return CFQ_KEY_ASYNC; } The following patch fixes the bug by adding sync parameter, wich is obtained through bio_sync macros. Signed-off-by: Vasily Tarasov <vtaras@openvz.org> -- --- ./block/cfq-iosched.c.syncwrite 2006-09-20 07:42:06.000000000 +0400 +++ ./block/cfq-iosched.c 2006-12-11 07:23:03.000000000 +0300 @@ -324,9 +324,9 @@ static int cfq_queue_empty(request_queue return !cfqd->busy_queues; } -static inline pid_t cfq_queue_pid(struct task_struct *task, int rw) +static inline pid_t cfq_queue_pid(struct task_struct *task, int rw, int sync) { - if (rw == READ || rw == WRITE_SYNC) + if (rw == READ || sync) return task->pid; return CFQ_KEY_ASYNC; @@ -621,7 +621,7 @@ static struct request * cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio) { struct task_struct *tsk = current; - pid_t key = cfq_queue_pid(tsk, bio_data_dir(bio)); + pid_t key = cfq_queue_pid(tsk, bio_data_dir(bio), bio_sync(bio)); struct cfq_queue *cfqq; struct rb_node *n; sector_t sector; @@ -1958,7 +1958,8 @@ static int cfq_may_queue(request_queue_t * so just lookup a possibly existing queue, or return 'may queue' * if that fails */ - cfqq = cfq_find_cfq_hash(cfqd, cfq_queue_pid(tsk, rw), tsk->ioprio); + cfqq = cfq_find_cfq_hash(cfqd, cfq_queue_pid(tsk, rw, + bio_sync(bio)), tsk->ioprio); if (cfqq) { cfq_init_prio_data(cfqq); cfq_prio_boost(cfqq); @@ -2020,7 +2021,7 @@ cfq_set_request(request_queue_t *q, stru struct task_struct *tsk = current; struct cfq_io_context *cic; const int rw = rq_data_dir(rq); - pid_t key = cfq_queue_pid(tsk, rw); + pid_t key = cfq_queue_pid(tsk, rw, bio_sync(bio)); struct cfq_queue *cfqq; struct cfq_rq *crq; unsigned long flags;
creator: Vasily Tarasov
date: 2006-12-11T15:45:19-00:00

Re: [PATCH] cfq: wrong sync writes detection
type: item
description: On Mon, Dec 11 2006, Vasily Tarasov wrote: > CFQ I/O scheduler does the following actions to > find out whether the request is sync: > > rw = rq_data_dir(rq); => possible values for rw are 0 or 1 > > static inline pid_t cfq_queue_pid(struct task_struct *task, int rw) > { > if (rw == READ || rw == WRITE_SYNC) => second condition is always false > return task->pid; > > return CFQ_KEY_ASYNC; > } > > The following patch fixes the bug by adding sync parameter, > wich is obtained through bio_sync macros. Good catch! Applied. -- Jens Axboe
creator: Jens Axboe
date: 2006-12-11T16:07:11-00:00