On Thu, 12 Sep 2013, Mike Snitzer wrote:
> Make use of static keys to eliminate the relevant branch in clone_rq()
> when dm_mod's 'track_peak_rq_based_ios' paramter is set to 0 (disabled).
>
> Even if 'track_peak_rq_based_ios' is set to 0 it will not take effect
> until the next request-based table reload. Once it is disabled the
> 'peak_rq_based_ios' parameter will be reset to 0.
This patch changes it so that the value track_peak_rq_based_ios is sampled
only when reloading a table. I think it will be confusing to the user if
he changes the value, but the change doesn't take effect until something
reloads some table.
Mikulas
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> ---
> drivers/md/dm.c | 33 +++++++++++++++++++++++++++++++--
> 1 file changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index de83930..d9e38a7 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -19,6 +19,7 @@
> #include <linux/idr.h>
> #include <linux/hdreg.h>
> #include <linux/delay.h>
> +#include <linux/static_key.h>
>
> #include <trace/events/block.h>
>
> @@ -242,10 +243,14 @@ static unsigned reserved_rq_based_ios_latch;
> * Optionally track the maximum numbers of IOs in a cloned request.
> */
> static unsigned track_peak_rq_based_ios;
> +static unsigned track_peak_rq_based_ios_latch;
> static unsigned peak_rq_based_ios;
>
> +static struct static_key_deferred track_peak_rq_based_ios_enabled; /* defaults to false */
> +
> /*
> - * This mutex protects reserved_bio_based_ios_latch and reserved_rq_based_ios_latch.
> + * This mutex protects reserved_bio_based_ios_latch, reserved_rq_based_ios_latch
> + * and track_peak_rq_based_ios_latch.
> */
> static DEFINE_MUTEX(dm_mempools_lock);
>
> @@ -305,6 +310,26 @@ unsigned dm_get_reserved_rq_based_ios(void)
> }
> EXPORT_SYMBOL_GPL(dm_get_reserved_rq_based_ios);
>
> +static void __track_peak_rq_based_ios_refresh(void)
> +{
> + bool enabled = static_key_false(&track_peak_rq_based_ios_enabled.key);
> +
> + BUG_ON(!mutex_is_locked(&dm_mempools_lock));
> +
> + track_peak_rq_based_ios_latch = ACCESS_ONCE(track_peak_rq_based_ios);
> +
> + if (track_peak_rq_based_ios_latch) {
> + if (enabled)
> + return; /* already enabled */
> + static_key_slow_inc(&track_peak_rq_based_ios_enabled.key);
> + } else {
> + if (!enabled)
> + return; /* already disabled */
> + static_key_slow_dec(&track_peak_rq_based_ios_enabled.key);
> + ACCESS_ONCE(peak_rq_based_ios) = 0;
> + }
> +}
> +
> static int __init local_init(void)
> {
> int r = -ENOMEM;
> @@ -1725,7 +1750,7 @@ static struct request *clone_rq(struct request *rq, struct mapped_device *md,
> return NULL;
> }
>
> - if (unlikely(ACCESS_ONCE(track_peak_rq_based_ios))) {
> + if (static_key_false(&track_peak_rq_based_ios_enabled.key)) {
> struct bio *bio;
> unsigned num_bios = 0;
>
> @@ -2984,6 +3009,10 @@ struct dm_md_mempools *dm_alloc_md_mempools(unsigned type, unsigned integrity, u
> if (reserved_rq_based_ios != reserved_rq_based_ios_latch)
> __reserved_request_based_ios_refresh();
> pool_size = reserved_rq_based_ios_latch;
> +
> + /* Check if track_peak_rq_based_ios changed. */
> + if (track_peak_rq_based_ios != track_peak_rq_based_ios_latch)
> + __track_peak_rq_based_ios_refresh();
> mutex_unlock(&dm_mempools_lock);
>
> front_pad = offsetof(struct dm_rq_clone_bio_info, clone);
> --
> 1.8.1.4
>
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