There's a race condition (it's not serious):
+ if (num_bios > ACCESS_ONCE(peak_rq_based_ios))
+ ACCESS_ONCE(peak_rq_based_ios) = num_bios;
You can double-check it using code like this:
if (num_bios > ACCESS_ONCE(peak_rq_based_ios)) {
spin_lock_irqsave(&peak_rq_based_ios_lock, flags);
if (num_bios > peak_rq_based_ios)
peak_rq_based_ios = num_bios;
spin_unlock_irqrestore(&peak_rq_based_ios_lock, flags);
}
Maybe - reset the value peak_rq_based_ios if the user clears
track_peak_rq_based_ios?
Mikulas
On Thu, 12 Sep 2013, Mike Snitzer wrote:
> If /sys/modules/dm_mod/parameters/track_peak_rq_based_ios is set to 1 it
> enables the tracking of the maximum number of bios in a cloned request.
>
> The maximum number of bios in a cloned request is then exposed through
> the following read-only parameter:
> /sys/modules/dm_mod/parameters/peak_rq_based_ios
>
> This information can be useful when deciding on a value for dm_mod's
> 'reserved_rq_based_ios' parameter. Otherwise, 'track_peak_rq_based_ios'
> should be kept disabled (the default).
>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> ---
> drivers/md/dm.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 186f77d..de83930 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -239,6 +239,12 @@ static unsigned reserved_rq_based_ios;
> 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 peak_rq_based_ios;
> +
> +/*
> * This mutex protects reserved_bio_based_ios_latch and reserved_rq_based_ios_latch.
> */
> static DEFINE_MUTEX(dm_mempools_lock);
> @@ -1719,6 +1725,16 @@ static struct request *clone_rq(struct request *rq, struct mapped_device *md,
> return NULL;
> }
>
> + if (unlikely(ACCESS_ONCE(track_peak_rq_based_ios))) {
> + struct bio *bio;
> + unsigned num_bios = 0;
> +
> + __rq_for_each_bio(bio, clone)
> + num_bios++;
> + if (num_bios > ACCESS_ONCE(peak_rq_based_ios))
> + ACCESS_ONCE(peak_rq_based_ios) = num_bios;
> + }
> +
> return clone;
> }
>
> @@ -3034,6 +3050,12 @@ MODULE_PARM_DESC(reserved_bio_based_ios, "Reserved IOs in bio-based mempools");
> module_param(reserved_rq_based_ios, uint, S_IRUGO | S_IWUSR);
> MODULE_PARM_DESC(reserved_rq_based_ios, "Reserved IOs in request-based mempools");
>
> +module_param(track_peak_rq_based_ios, uint, S_IRUGO | S_IWUSR);
> +MODULE_PARM_DESC(peak_rq_based_ios, "Enable tracking the maximum IOs in a cloned request");
> +
> +module_param(peak_rq_based_ios, uint, S_IRUGO);
> +MODULE_PARM_DESC(peak_rq_based_ios, "Tracks the maximum IOs in a cloned request");
> +
> MODULE_DESCRIPTION(DM_NAME " driver");
> MODULE_AUTHOR("Joe Thornber <dm-devel@xxxxxxxxxx>");
> MODULE_LICENSE("GPL");
> --
> 1.8.1.4
>
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