[+tytso]
Hi Theodore,
in order to fix a performance problem with fsync in cfq, we need to
mark write requests sent by jbd/jbd2 as synchronous, so cfq knows that
some process may be waiting on them, and therefore will avoid idling.
Is this change reasonable for you? Should I send the change to
jbd*/commit.cc in a separated patch through your tree?

Thanks
Corrado

On Tue, Jul 20, 2010 at 10:09 PM, Corrado Zoccolo <czoccolo@gmail.com> wrote:
quoted text
> Fsync performance for small files achieved by cfq on high-end disks is
> lower than what deadline can achieve, due to idling introduced between
> the sync write happening in process context and the journal commit.
>
> Moreover, when competing with a sequential reader, a process writing
> small files and fsync-ing them is starved.
>
> This patch fixes the two problems by:
> - marking journal commits as WRITE_SYNC, so that they get the REQ_NOIDLE
>  flag set,
> - force all queues that have REQ_NOIDLE requests to be put in the noidle
>  tree.
>
> Having the queue associated to the fsync-ing process and the one associated
>  to journal commits in the noidle tree allows:
> - switching between them without idling,
> - fairness vs. competing idling queues, since they will be serviced only
>  after the noidle tree expires its slice.
>
> Acked-by: Vivek Goyal <vgoyal@redhat.com>
> Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
> Tested-by: Jeff Moyer <jmoyer@redhat.com>
> Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
> ---
>  block/cfq-iosched.c |   18 ++++--------------
>  fs/jbd/commit.c     |    2 +-
>  fs/jbd2/commit.c    |    2 +-
>  3 files changed, 6 insertions(+), 16 deletions(-)
>
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index eb4086f..49dada4 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -216,7 +216,6 @@ struct cfq_data {
>        enum wl_type_t serving_type;
>        unsigned long workload_expires;
>        struct cfq_group *serving_group;
> -       bool noidle_tree_requires_idle;
>
>        /*
>         * Each priority tree is sorted by next_request position.  These
> @@ -2126,7 +2125,6 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
>        slice = max_t(unsigned, slice, CFQ_MIN_TT);
>        cfq_log(cfqd, "workload slice:%d", slice);
>        cfqd->workload_expires = jiffies + slice;
> -       cfqd->noidle_tree_requires_idle = false;
>  }
>
>  static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
> @@ -3108,7 +3106,9 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>        if (cfqq->queued[0] + cfqq->queued[1] >= 4)
>                cfq_mark_cfqq_deep(cfqq);
>
> -       if (!atomic_read(&cic->ioc->nr_tasks) || !cfqd->cfq_slice_idle ||
> +       if (cfqq->next_rq && (cfqq->next_rq->cmd_flags & REQ_NOIDLE))
> +               enable_idle = 0;
> +       else if (!atomic_read(&cic->ioc->nr_tasks) || !cfqd->cfq_slice_idle ||
>            (!cfq_cfqq_deep(cfqq) && CFQQ_SEEKY(cfqq)))
>                enable_idle = 0;
>        else if (sample_valid(cic->ttime_samples)) {
> @@ -3421,17 +3421,7 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
>                        cfq_slice_expired(cfqd, 1);
>                else if (sync && cfqq_empty &&
>                         !cfq_close_cooperator(cfqd, cfqq)) {
> -                       cfqd->noidle_tree_requires_idle |=
> -                               !(rq->cmd_flags & REQ_NOIDLE);
> -                       /*
> -                        * Idling is enabled for SYNC_WORKLOAD.
> -                        * SYNC_NOIDLE_WORKLOAD idles at the end of the tree
> -                        * only if we processed at least one !REQ_NOIDLE request
> -                        */
> -                       if (cfqd->serving_type == SYNC_WORKLOAD
> -                           || cfqd->noidle_tree_requires_idle
> -                           || cfqq->cfqg->nr_cfqq == 1)
> -                               cfq_arm_slice_timer(cfqd);
> +                       cfq_arm_slice_timer(cfqd);
>                }
>        }
>
> diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
> index 28a9dda..d97a0c6 100644
> --- a/fs/jbd/commit.c
> +++ b/fs/jbd/commit.c
> @@ -317,7 +317,7 @@ void journal_commit_transaction(journal_t *journal)
>        int first_tag = 0;
>        int tag_flag;
>        int i;
> -       int write_op = WRITE;
> +       int write_op = WRITE_SYNC;
>
>        /*
>         * First job: lock down the current transaction and wait for
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index 75716d3..a078744 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -369,7 +369,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
>        int tag_bytes = journal_tag_bytes(journal);
>        struct buffer_head *cbh = NULL; /* For transactional checksums */
>        __u32 crc32_sum = ~0;
> -       int write_op = WRITE;
> +       int write_op = WRITE_SYNC;
>
>        /*
>         * First job: lock down the current transaction and wait for
> --
> 1.6.2.5
>
>
>



-- 
__________________________________________________________________________

dott. Corrado Zoccolo                          mailto:czoccolo@gmail.com
PhD - Department of Computer Science - University of Pisa, Italy
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