linux-kernel - Re: [PATCH 3/6 v4] cfq-iosched: Introduce vdisktime and io weight for CFQ queue

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Date:	Mon, 14 Feb 2011 11:58:03 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Gui Jianfeng <guijianfeng@...fujitsu.com>
Cc:	Jens Axboe <axboe@...nel.dk>, Shaohua Li <shaohua.li@...el.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Chad Talbott <ctalbott@...gle.com>,
	Divyesh Shah <dpshah@...gle.com>
Subject: Re: [PATCH 3/6 v4] cfq-iosched: Introduce vdisktime and io weight
 for CFQ queue

On Sat, Feb 12, 2011 at 09:20:58AM +0800, Gui Jianfeng wrote:
> Vivek Goyal wrote:
> > On Thu, Feb 10, 2011 at 03:47:16PM +0800, Gui Jianfeng wrote:
> >> Introduce vdisktime and io weight for CFQ queue scheduling. Currently, io priority
> >> maps to a range [100,1000]. It also gets rid of cfq_slice_offset() logic and makes
> >> use the same scheduling algorithm as CFQ group does. This helps for CFQ queue and
> >> group scheduling on the same service tree.
> >>
> >> Signed-off-by: Gui Jianfeng <guijianfeng@...fujitsu.com>
> >> ---
> >>  block/cfq-iosched.c |  219 +++++++++++++++++++++++++++++++++++++++------------
> >>  1 files changed, 167 insertions(+), 52 deletions(-)
> >>
> >> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> >> index f3a126e..41cef2e 100644
> >> --- a/block/cfq-iosched.c
> >> +++ b/block/cfq-iosched.c
> >> @@ -39,6 +39,13 @@ static const int cfq_hist_divisor = 4;
> >>   */
> >>  #define CFQ_IDLE_DELAY		(HZ / 5)
> >>  
> >> +/* 
> >> + * The base boosting value.
> >> + */
> >> +#define CFQ_BOOST_SYNC_BASE          (HZ / 10)
> >> +#define CFQ_BOOST_ASYNC_BASE          (HZ / 25)
> >> +
> > 
> > These are same as cfq_slice_sync and cfq_slice_async. Looking at
> > boost logic, this is equivalent of starting a new queue/group as
> > if it is being requeued after conuming a full slice. So may be we can divide
> > it by some const number say 4 or something like that. This is a minor
> > point though as this algorimthm will kind of evolve and we will learn
> > what works best.
> > 
> > Secondly, I think you wanted to SYNC vs ASYNC logic seem to be reversed.
> > We would like to give ASYNC queues higher boost (Put these farther in 
> > tree) and lesser boost to SYNC queues. Looks like above constants will
> > do the reverse? 
> 
> Hi Vivek,
> 
> Currently, SYNC and ASYNC queues are in different service tree, they don't
> impact each other. Here, I Really want use this logic.

Ok, SYNC and ASYNC are on separate service tree so their vtime are not
comparable (as of today, down the line one might want to look at those for
better workload selection logic).

Anyway, because two are on seprate tree so why should we have separate
boosting constants for them? How does it help?

Thanks
Vivek
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