linux-kernel - Re: [patch 13/15] sched: add exports tracking cfs bandwidth control statistics

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Date:	Wed, 11 May 2011 16:56:34 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	Paul Turner <pjt@...gle.com>
CC:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Dhaval Giani <dhaval.giani@...il.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Nikhil Rao <ncrao@...gle.com>
Subject: Re: [patch 13/15] sched: add exports tracking cfs bandwidth control
 statistics

Oops, I found an issue here.

(2011/05/03 18:28), Paul Turner wrote:
> @@ -1628,6 +1631,12 @@ retry:
>  		raw_spin_unlock(&cfs_b->lock);
>  		goto retry;
>  	}
> +
> +	/* update throttled stats */
> +	cfs_b->nr_periods += overrun;
> +	if (throttled)
> +		cfs_b->nr_throttled += overrun;
> +
>  	cfs_b->runtime = runtime;
>  	cfs_b->idle = idle;
>  out_unlock:

Quoting from patch 09/15:

+	if (!throttled || quota == RUNTIME_INF)
+		goto out;
+	idle = 0;
+
+retry:
+	runtime = distribute_cfs_runtime(cfs_b, runtime, runtime_expires);
+
+	raw_spin_lock(&cfs_b->lock);
+	/* new new bandwidth may have been set */
+	if (unlikely(runtime_expires != cfs_b->runtime_expires))
+		goto out_unlock;
+	/*
+	 * make sure no-one was throttled while we were handing out the new
+	 * runtime.
+	 */
+	if (runtime > 0 && !list_empty(&cfs_b->throttled_cfs_rq)) {
+		raw_spin_unlock(&cfs_b->lock);
+		goto retry;
+	}
+	cfs_b->runtime = runtime;
+	cfs_b->idle = idle;
+out_unlock:
+	raw_spin_unlock(&cfs_b->lock);
+out:

Since we skip distributing runtime (by "goto out") when !throttled,
the new block inserted by this patch is passed only when throttled.
So I see that nr_periods and nr_throttled look the same.

Maybe we should move this block up like followings.

Thanks,
H.Seto

---
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1620,6 +1620,12 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
 		idle = cfs_b->idle;
 		cfs_b->idle = 1;
 	}
+
+	/* update throttled stats */
+	cfs_b->nr_periods += overrun;
+	if (throttled)
+		cfs_b->nr_throttled += overrun;
+
 	raw_spin_unlock(&cfs_b->lock);
 
 	if (!throttled || quota == RUNTIME_INF)
@@ -1642,11 +1648,6 @@ retry:
 		goto retry;
 	}
 
-	/* update throttled stats */
-	cfs_b->nr_periods += overrun;
-	if (throttled)
-		cfs_b->nr_throttled += overrun;
-
 	cfs_b->runtime = runtime;
 	cfs_b->idle = idle;
 out_unlock:


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