On 12/5/18 11:18 AM, Mike Snitzer wrote: > On Wed, Dec 05 2018 at 1:04pm -0500, > Jens Axboe <axboe@xxxxxxxxx> wrote: > >> On 12/5/18 11:03 AM, Mike Snitzer wrote: >>> On Wed, Dec 05 2018 at 12:54pm -0500, >>> Jens Axboe <axboe@xxxxxxxxx> wrote: >>> >>>> On 12/5/18 10:49 AM, Mike Snitzer wrote: >>>>> On Wed, Dec 05 2018 at 12:30pm -0500, >>>>> Jens Axboe <axboe@xxxxxxxxx> wrote: >>>>> >>>>>> There's also no need to pass in the cpu, if we're not running with >>>>>> preempt disabled already we have a problem. >>>>> >>>>> Why should this be any different than the part_stat_* interfaces? >>>>> __part_stat_add(), part_stat_read(), etc also use >>>>> per_cpu_ptr((part)->dkstats, (cpu) accessors. >>>> >>>> Maybe audit which ones actually need it? To answer the specific question, >>>> it's silly to pass in the cpu, if we're pinned already. That's true >>>> both programatically, but also for someone reading the code. >>> >>> I understand you'd like to avoid excess interface baggage. But seems to >>> me we'd be better off being consistent, when extending the percpu >>> portion of block core stats, and then do an incremental to clean it all >>> up. >> >> The incremental should be done first in that case, it'd be silly to >> introduce something only to do a cleanup right after. > > OK, all existing code for these percpu stats should follow the pattern: > > int cpu = part_stat_lock(); > > <do percpu diskstats stuff> > > part_stat_unlock(); > > part_stat_lock() calls get_cpu() which does preempt_disable(). So to > your point: yes we have preempt disabled. And yes we _could_ just use > smp_processor_id() in callers rather than pass 'cpu' to them. > > Is that what you want to see? Something like that, yes. -- Jens Axboe
