On Thu, Sep 12 2013 at 7:30pm -0400, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > On Thu, 12 Sep 2013, Mike Snitzer wrote: > > > On Thu, Sep 12 2013 at 7:00pm -0400, > > Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > > > > > > > > > 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. > > > > Well we need to be able to notice the change but I do not wish to do so > > in a performance critical path (which clone_rq is). > > I think one condition isn't that bad so there is no need to use static > keys. Considering we're talking about the IO path I'd rather avoid it given 'track_peak_rq_based_ios' will almost always be disabled. > If you want to use static keys, you need to refresh them in some place > that it called regularly. No you don't. I'm assuming if someone enables 'track_peak_rq_based_ios' they know what they are doing. But I'm open to suggestions on a more appropriate hook to be catching the update to track_peak_rq_based_ios. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
