From: Vivek Goyal <vgoyal@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk, ctalbott@google.com, rni@google.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH UPDATED 11/11] blkcg: unify blkg's for blkcg policies
Date: Fri, 3 Feb 2012 17:23:29 -0500 [thread overview]
Message-ID: <20120203222329.GG9683@redhat.com> (raw)
In-Reply-To: <20120203221409.GF14209@google.com>
On Fri, Feb 03, 2012 at 02:14:09PM -0800, Tejun Heo wrote:
> On Fri, Feb 03, 2012 at 04:53:49PM -0500, Vivek Goyal wrote:
> > Hmm... then blkiocg_reset_stats() will run into lock ordering issue. Can't
> > hold queue lock inside blkcg lock. I guess you will do some kind of
> > locking trick again as you did for io context logic.
>
> Ummm... I don't know the details yet but decisions like making
> policies per-queue are much higher level than locking details. There
> are cases where implementation details become problematic enough and
> high level decisions are affected but I don't really think that would
> be the case here. It's not like reset stats is a hot path. In fact,
> I don't even understand why the hell we have it. I guess it's another
> blkcg braindamage.
git commit of when it was added.
commit 84c124da9ff50bd71fab9c939ee5b7cd8bef2bd9
Author: Divyesh Shah <dpshah@google.com>
Date: Fri Apr 9 08:31:19 2010 +0200
..
o add a separate reset_stats interface
..
>
> If userland is interested in delta between certain periods, it's
> supposed to read values at the start and end of the period and
> subtract. Allowing reset might make sense if there's single bearded
> admin looking at the raw numbers, but it breaks as soon as tools and
> automation are involved. How would you decide who owns those
> counters?
>
Personally I consider it to be a debugging aid. User space applications
should do what you suggested and that is take delta between certain
periods.
Frankly speaking I have found it useful though. If I am debugging something,
I don't have to reboot the system to reset the stats and calculating the
difference from zero is easier for humans.
Thanks
Vivek
next prev parent reply other threads:[~2012-02-03 22:23 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-01 21:19 [PATCHSET] blkcg: unify blkgs for different policies Tejun Heo
2012-02-01 21:19 ` [PATCH 01/11] blkcg: let blkio_group point to blkio_cgroup directly Tejun Heo
2012-02-02 20:03 ` Vivek Goyal
2012-02-02 20:33 ` Tejun Heo
2012-02-02 20:55 ` Vivek Goyal
2012-02-01 21:19 ` [PATCH 02/11] block: relocate elevator initialized test from blk_cleanup_queue() to blk_drain_queue() Tejun Heo
2012-02-02 20:20 ` Vivek Goyal
2012-02-02 20:35 ` Tejun Heo
2012-02-02 20:37 ` Vivek Goyal
2012-02-02 20:38 ` Tejun Heo
2012-02-01 21:19 ` [PATCH 03/11] blkcg: add blkcg_{init|drain|exit}_queue() Tejun Heo
2012-02-01 21:19 ` [PATCH 04/11] blkcg: clear all request_queues on blkcg policy [un]registrations Tejun Heo
2012-02-01 21:19 ` [PATCH 05/11] blkcg: let blkcg core handle policy private data allocation Tejun Heo
2012-02-01 21:19 ` [PATCH 06/11] blkcg: move refcnt to blkcg core Tejun Heo
2012-02-02 22:07 ` Vivek Goyal
2012-02-02 22:11 ` Tejun Heo
2012-02-01 21:19 ` [PATCH 07/11] blkcg: make blkg->pd an array and move configuration and stats into it Tejun Heo
2012-02-01 21:19 ` [PATCH 08/11] blkcg: don't use blkg->plid in stat related functions Tejun Heo
2012-02-01 21:19 ` [PATCH 09/11] blkcg: move per-queue blkg list heads and counters to queue and blkg Tejun Heo
2012-02-02 22:47 ` Vivek Goyal
2012-02-02 22:47 ` Tejun Heo
2012-02-01 21:19 ` [PATCH 10/11] blkcg: let blkcg core manage per-queue blkg list and counter Tejun Heo
2012-02-01 21:19 ` [PATCH 11/11] blkcg: unify blkg's for blkcg policies Tejun Heo
2012-02-02 0:37 ` [PATCH UPDATED " Tejun Heo
2012-02-03 19:41 ` Vivek Goyal
2012-02-03 20:59 ` Tejun Heo
2012-02-03 21:44 ` Vivek Goyal
2012-02-03 21:47 ` Tejun Heo
2012-02-03 21:53 ` Vivek Goyal
2012-02-03 22:14 ` Tejun Heo
2012-02-03 22:23 ` Vivek Goyal [this message]
2012-02-03 22:28 ` Tejun Heo
2012-02-03 21:06 ` Vivek Goyal
2012-02-03 21:09 ` Tejun Heo
2012-02-03 21:10 ` Tejun Heo
2012-02-14 1:33 ` [PATCH UPDATED2 " Tejun Heo
2012-02-15 17:02 ` Vivek Goyal
2012-02-16 22:42 ` Tejun Heo
2012-02-02 19:29 ` [PATCHSET] blkcg: unify blkgs for different policies Vivek Goyal
2012-02-02 20:36 ` Tejun Heo
2012-02-02 20:43 ` Vivek Goyal
2012-02-02 20:59 ` Tejun Heo
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=20120203222329.GG9683@redhat.com \
--to=vgoyal@redhat.com \
--cc=axboe@kernel.dk \
--cc=ctalbott@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=rni@google.com \
--cc=tj@kernel.org \
/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
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).