Messages in this thread | | | Date | Wed, 04 Jun 2014 20:16:32 -0600 | From | Jens Axboe <> | Subject | Re: [PATCH] block: per-cpu counters for in-flight IO accounting |
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On 2014-06-04 20:09, Shaohua Li wrote: > On Wed, Jun 04, 2014 at 02:08:46PM -0600, Jens Axboe wrote: >> On 06/04/2014 05:29 AM, Matias Bjørling wrote: >>> It's in >>> >>> blk_io_account_start >>> part_round_stats >>> part_round_state_single >>> part_in_flight >>> >>> I like the granularity idea. >> >> And similarly from blk_io_account_done() - which makes it even worse, >> since it at both ends of the IO chain. > > But part_round_state_single is supposed to only call part_in_flight every > jiffery. Maybe we need something below: > 1. set part->stamp immediately > 2. fixed granularity > Untested though. > > > diff --git a/block/blk-core.c b/block/blk-core.c > index 40d6548..5f0acaa 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -1270,17 +1270,19 @@ static void part_round_stats_single(int cpu, struct hd_struct *part, > unsigned long now) > { > int inflight; > + unsigned long old_stamp; > > - if (now == part->stamp) > + if (time_before(now, part->stamp + msecs_to_jiffies(10))) > return; > + old_stamp = part->stamp; > + part->stamp = now; > > inflight = part_in_flight(part); > if (inflight) { > __part_stat_add(cpu, part, time_in_queue, > - inflight * (now - part->stamp)); > - __part_stat_add(cpu, part, io_ticks, (now - part->stamp)); > + inflight * (now - old_stamp)); > + __part_stat_add(cpu, part, io_ticks, (now - old_stamp)); > } > - part->stamp = now; > } > > /**
It'd be a good improvement, and one we should be able to do without screwing anything up. It'd be identical to anyone running at HZ==100 right now.
So the above we can easily do, and arguably should just do. We wont see real scaling in the IO stats path before we fixup the hd_struct referencing as well, however.
-- Jens Axboe
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