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

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Date:	Thu, 5 Jun 2014 10:09:34 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Matias Bjørling <m@...rling.me>,
	"Sam Bradshaw (sbradshaw)" <sbradshaw@...ron.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block: per-cpu counters for in-flight IO accounting

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;
 }
 
 /**
--
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