Messages in this thread | | | Date | Thu, 5 Jun 2014 10:33:34 +0800 | From | Shaohua Li <> | Subject | Re: [PATCH] block: per-cpu counters for in-flight IO accounting |
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On Wed, Jun 04, 2014 at 08:16:32PM -0600, Jens Axboe wrote: > 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.
That's true. maybe a percpu_ref works here.
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