archive mirror
 help / color / mirror / Atom feed
From: Tao Ma <>
To: Tejun Heo <>
Cc:, Vivek Goyal <>,
	Jens Axboe <>
Subject: Re: [PATCH V2] block/throttle: Add IO throttled information in blkio.throttle.
Date: Sat, 01 Sep 2012 21:58:43 +0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Hi Tejun,
On 09/01/2012 09:05 AM, Tejun Heo wrote:
> On Fri, Aug 31, 2012 at 01:15:09PM +0800, Tao Ma wrote:
>> From: Tao Ma <>
>> Currently, if the IO is throttled by io-throttle, the SA has no idea of
> What's SA?
system admin.
>> the situation and can't report it to the real application user about
>> that he/she has to do something. So this patch adds a new interface
> Why does the application user "has to" do something?  There's nothing
> the upper layer "must" do.  I'm not necessarily objecting to adding
> the stat but the description seems a bit misleading.
>> named blkio.throttle.io_queued which indicates how many IOs are
>> currently throttled.
> Also, the suggested stat is rather lacking for such purposes.  There's
> no way other than keeping polling to find out the condition, which is
> rather sad.  What's the actual use case here?
Vivek and I have talked about its usage in my first try. See the thread
And I am OK to say it again here. In our case, we use flashcache as a
block device and the bad thing is that flashcache is a bio-based dm
target and we can't use block io controller here to control the weight
of different cgroups. So io throttle is chosen. But as io throttle can
only set a hard upper limit for different instances, it makes the
control not flexible enough. Say with io controller, if there is no
requests form the cgroup with weight 1000, a cgroup with 500 can use the
whole bandwidth of the underlying device. But if we set 1000 iops for
cgroup A and 500 iops for cgroup B in io throttle, cgroup B can't exceed
its limit even if cgroup A has no request pending. So if we can export
the io_queued information out to the system admin, they can write some
daemon and in the above case, increase the upper limit of cgroup B to
some number say 1000. It helps us to utilize the device more
efficiently. Does it make sense to you?

>> Also another function blkg_rwstat_dec is added since the number of throttled
>> IOs can be either added or decreased.
> Maybe just make blkg_rwstat_add() to take int64_t instead of uint64_t?
sure, will change it in the later version.
>> +static void throtl_update_queued_stats(struct throtl_grp *tg, int rw, int add)
>> +{
>> +	struct tg_stats_cpu *stats_cpu;
>> +	unsigned long flags;
>> +
>> +	/* If per cpu stats are not allocated yet, don't do any accounting. */
>> +	if (tg->stats_cpu == NULL)
>> +		return;
>> +
>> +	/*
>> +	 * Disabling interrupts to provide mutual exclusion between two
>> +	 * writes on same cpu. It probably is not needed for 64bit. Not
>> +	 * optimizing that case yet.
>> +	 */
>> +	local_irq_save(flags);
>> +
>> +	stats_cpu = this_cpu_ptr(tg->stats_cpu);
>> +	if (add)
>> +		blkg_rwstat_add(&stats_cpu->io_queued, rw, 1);
>> +	else
>> +		blkg_rwstat_dec(&stats_cpu->io_queued, rw, 1);
>> +
>> +	local_irq_restore(flags);
> Adding throttle.io_queued could be a bit more consistent?
sorry, I don't know what is your meaning here. You mean some codes like
	blkg_rwstat_add(&stats_cpu->throttle.io_queude, rw, 1)?


  reply	other threads:[~2012-09-01 13:58 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-31  5:15 [PATCH V2] block/throttle: Add IO throttled information in blkio.throttle Tao Ma
2012-09-01  1:05 ` Tejun Heo
2012-09-01 13:58   ` Tao Ma [this message]
2012-09-04 19:13     ` Tejun Heo
2012-09-04 13:35 ` Vivek Goyal
2012-09-04 14:12   ` Tao Ma
2012-09-04 14:23     ` Vivek Goyal
2012-09-04 14:45     ` Vivek Goyal

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:

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

  git send-email \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
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).