linux-kernel - Re: [PATCH] cfq-iosched: convert slice idle time to jiffies

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Message-ID: <5682C095.70002@kernel.dk>
Date:	Tue, 29 Dec 2015 10:19:17 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Alexandru Moise <00moses.alexander00@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cfq-iosched: convert slice idle time to jiffies

On 12/28/2015 06:08 PM, Alexandru Moise wrote:
> This patch refers to Jens Axboe's change way back in 2006:
> 7b14e3b52 cfq-iosched: slice expiry fixups
>
> In this patch he fixed a potential timer race condition by delaying
> idle_slice_timer by the slice_idle time value.
>
> Today this timer is delayed by either slice_idle or group_idle time
> values, which on my system, and according to
> Documentation/block/cfq-iosched.txt the default value for both is 8ms.
>
> Since the time given by either variables is supposed to be in
> milliseconds we should convert that value from milliseconds to jiffies
> before adding it to jiffies variable and setting our timer.
>
> In my obervations the area is really active as I've seen that function
> get called a lot for each device on my btrfs raid setup during btrfs
> check. I've also timed the btrfs check before and after applying the
> patch and I might've noticed a very slight improvement in execution
> time but the numbers vary too much for me to post any believable
> numbers (10 milliseconds difference at most on average).

cfqd->cfq_slice_idle is in jiffies, it's not in msecs.

-- 
Jens Axboe

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