linux-kernel - RE: RFC: I/O bandwidth controller

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Message-ID: <D1D4C3FF75F9354393DB8314DF43DEF2E7F7ED@xbl3.emulex.com>
Date:	Tue, 12 Aug 2008 11:03:24 -0400
From:	James.Smart@...lex.Com
To:	<fernando@....ntt.co.jp>, <righi.andrea@...il.com>
Cc:	<xen-devel@...ts.xensource.com>,
	<containers@...ts.linux-foundation.org>,
	<linux-kernel@...r.kernel.org>,
	<virtualization@...ts.linux-foundation.org>, <taka@...inux.co.jp>,
	<dm-devel@...hat.com>, <agk@...rceware.org>,
	<baramsori72@...il.com>, <dave@...ux.vnet.ibm.com>,
	<ngupta@...gle.com>, <balbir@...ux.vnet.ibm.com>
Subject: RE: RFC: I/O bandwidth controller

Fernando Luis Vázquez Cao wrote:
> > BTW as I said in a previous email, an interesting path to 
> be explored
> > IMHO could be to think in terms of IO time. So, look at the 
> time an IO
> > request is issued to the drive, look at the time the 
> request is served,
> > evaluate the difference and charge the consumed IO time to the
> > appropriate cgroup. Then dispatch IO requests in function of the
> > consumed IO time debts / credits, using for example a token-bucket
> > strategy. And probably the best place to implement the IO time
> > accounting is the elevator.
> Please note that the seek time for a specific IO request is strongly
> correlated with the IO requests that preceded it, which means that the
> owner of that request is not the only one to blame if it 
> takes too long
> to process it. In other words, with the algorithm you propose 
> we may end
> up charging the wrong guy.

I assume all of these discussions are focused on simple storage - disks
direct attached to a single server - and are not targeted at SANs with
arrays, multi-initiator accesses, and fabric/network impacts. True ? 
Such algorithms can be seriously off-base in these latter configurations.

-- james s
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