Re: [PATCH] block: per-cpu counters for in-flight IO accounting

Shaohua Li
2014-06-05T02:09:43Z

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;
}

/**