LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Vivek Goyal <vgoyal@redhat.com>
To: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux kernel mailing list <linux-kernel@vger.kernel.org>,
	Corrado Zoccolo <czoccolo@gmail.com>,
	Chad Talbott <ctalbott@google.com>,
	Nauman Rafique <nauman@google.com>,
	Divyesh Shah <dpshah@google.com>,
	jmoyer@redhat.com, Shaohua Li <shaohua.li@intel.com>
Subject: Re: [PATCH 3/6 v3] cfq-iosched: Introduce vdisktime and io weight for CFQ queue
Date: Wed, 19 Jan 2011 17:58:55 -0500	[thread overview]
Message-ID: <20110119225855.GH13887@redhat.com> (raw)
In-Reply-To: <4D185374.6090300@cn.fujitsu.com>

On Mon, Dec 27, 2010 at 04:51:00PM +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@cn.fujitsu.com>

[..]
> @@ -1246,47 +1278,71 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
>  
>  	service_tree = service_tree_for(cfqq->cfqg, cfqq_prio(cfqq),
>  						cfqq_type(cfqq));
> +	/*
> +	 * For the time being, put the newly added CFQ queue at the end of the
> +	 * service tree.
> +	 */
> +	if (RB_EMPTY_NODE(&cfqe->rb_node)) {
> +		/*
> +		 * If this CFQ queue moves to another group, the original
> +		 * vdisktime makes no sense any more, reset the vdisktime
> +		 * here.
> +		 */
> +		parent = rb_last(&service_tree->rb);
> +		if (parent) {
> +			u64 boost;
> +			s64 __vdisktime;
> +
> +			__cfqe = rb_entry_entity(parent);
> +			cfqe->vdisktime = __cfqe->vdisktime + CFQ_IDLE_DELAY;
> +
> +			/* Give some vdisktime boost according to its weight */
> +			boost = cfq_get_boost(cfqd, cfqe);
> +			__vdisktime = cfqe->vdisktime - boost;
> +			if (__vdisktime > service_tree->min_vdisktime)
> +				cfqe->vdisktime = __vdisktime;
> +			else
> +				cfqe->vdisktime = service_tree->min_vdisktime;
> +		} else
> +			cfqe->vdisktime = service_tree->min_vdisktime;

Hi Gui,

Is above logic actually working? I suspect that most of the time all the
new queues will end up getting same vdisktime and that is st->min_vdisktime
and there will be no service differentiation across various prio.

Reason being, on SSD, idle is disabled. So very few/no queue will consume
its slice and follow reque path. So every queue will be new. Now you are
doing following.

	cfqd->vdisktime = vdisktime_of_parent + IDLE_DELAY - boost

assume vdisktime_of_parent=st->min_vdisktime, then (IDLE_DELAY - boost)
is always going to be a -ve number and hence cfqd->vdisktime will 
default to st->min_vdisktime. (IDLE_DELAY=200 while boost should be a huge
value due to SERVICE_SHIFT thing).

I think this logic needs refining. Maybe instead of subtracting the boost
we can instead place entities further away from st->min_vdisktime and
offset is higher for lower ioprio queues.

	cfqe->vdisktime = st->min_vdisktime + offset

here offset is something similar to boost but reversed in nature in the
sense that lower weight has got lower offset and vice-versa.

The important test here will be to run bunch of cfqq queues of different 
ioprio on a SSD with queue depth 1 and see if you can see the service
differentiation. If yes, then you can increase the queue depth a bit
and also number of competing queues and see what's the result. Also 
monitor the blktrace and vdisktime and make sure higher prio queues
get to run more than lower prio queues.

This is the most critical piece of converting cfqq scheduling logic,
so lets make sure that we get it right.


Thanks
Vivek

  parent reply	other threads:[~2011-01-19 22:59 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <4D180ECE.4000305@cn.fujitsu.com>
2010-12-27  8:50 ` [PATCH 1/6 v3] cfq-iosched: Introduce cfq_entity " Gui Jianfeng
2010-12-27  8:50 ` [PATCH 2/6 v3] cfq-iosched: Introduce cfq_entity for CFQ group Gui Jianfeng
2011-01-18 21:20   ` Vivek Goyal
2011-01-19  1:25     ` Gui Jianfeng
2011-01-23  2:15     ` Gui Jianfeng
2010-12-27  8:51 ` [PATCH 3/6 v3] cfq-iosched: Introduce vdisktime and io weight for CFQ queue Gui Jianfeng
2010-12-28  2:50   ` Shaohua Li
2010-12-28  3:59     ` Gui Jianfeng
2010-12-28  6:03       ` Shaohua Li
2010-12-28  6:59         ` Gui Jianfeng
2011-01-19 22:58   ` Vivek Goyal [this message]
2011-01-20  3:58     ` Gui Jianfeng
2011-01-20 11:09       ` Vivek Goyal
2011-01-24  4:45         ` Gui Jianfeng
2011-01-24 18:51           ` Vivek Goyal
2010-12-27  8:51 ` [PATCH 4/6 v3] cfq-iosched: Extract some common code of service tree handling for CFQ queue and CFQ group Gui Jianfeng
2010-12-27  8:51 ` [PATCH 5/6 v3] cfq-iosched: CFQ group hierarchical scheduling and use_hierarchy interface Gui Jianfeng
2011-01-24 22:52   ` Vivek Goyal
2010-12-27  8:51 ` [PATCH 6/6 v3] blkio-cgroup: Document for blkio.use_hierarchy interface Gui Jianfeng
2011-01-18 20:27   ` Vivek Goyal
2011-01-19  1:20     ` Gui Jianfeng

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20110119225855.GH13887@redhat.com \
    --to=vgoyal@redhat.com \
    --cc=axboe@kernel.dk \
    --cc=ctalbott@google.com \
    --cc=czoccolo@gmail.com \
    --cc=dpshah@google.com \
    --cc=guijianfeng@cn.fujitsu.com \
    --cc=jmoyer@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=nauman@google.com \
    --cc=shaohua.li@intel.com \
    --subject='Re: [PATCH 3/6 v3] cfq-iosched: Introduce vdisktime and io weight for CFQ queue' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).