linux-kernel - Re: [PATCH] Delay accounting, fix incorrect delay time when constantly waiting on runqueue

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Date:	Mon, 16 Jun 2008 22:04:46 +0530
From:	"Balbir Singh" <balbir@...ux.vnet.ibm.com>
To:	bharathravi1@...il.com
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org, peterz@...radead.org,
	dhaval@...ux.vnet.ibm.com, vatsa@...ibm.com,
	"Madhava K R" <madhavakr@...il.com>
Subject: Re: [PATCH] Delay accounting, fix incorrect delay time when constantly waiting on runqueue

On Mon, Jun 16, 2008 at 3:11 PM,  <bharathravi1@...il.com> wrote:
> From: Bharath Ravi <bharathravi1@...il.com>
>
> This patch corrects the incorrect value of per process run-queue wait time
> reported by delay statistics. The anomaly was due to the following reason.
> When a process leaves the CPU and immediately starts waiting for CPU on
> the runqueue (which means it remains in the TASK_RUNNABLE state), the time
> of re-entry into the run-queue is never recorded. Due to this, the waiting time
> on the runqueue from this point of re-entry upto the next time it hits the CPU
> is not accounted for. This is solved by recording the time of re-entry of a
> process leaving the CPU in the sched_info_depart() function IF the process will
> go back to waiting on the run-queue. This IF condition is verified by checking
> whether the process is still in the TASK_RUNNABLE state.
>
> The patch was tested on 2.6.26-rc6 using two simple CPU hog programs. The
> values noted prior to the fix did not account for the time spent on the
> runqueue waiting. After the fix, the correct values were reported back
> to user space.
>
> Signed-off-by: Bharath Ravi <bharathravi1@...il.com>
> Signed-off-by: Madhava K R  <madhavakr@...il.com>

Looks very good to me

Acked-by: Balbir Singh <balbir@...ux.vnet.ibm.com>

Balbir
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