linux-kernel - Re: request->ioprio

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Message-Id: <1218688006.30624.9.camel@sebastian.kern.oss.ntt.co.jp>
Date:	Thu, 14 Aug 2008 13:26:46 +0900
From:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
	吉川 拓哉 
	<yoshikawa.takuya@....ntt.co.jp>, dpshah@...gle.com
Subject: Re: request->ioprio

On Thu, 2008-08-14 at 12:16 +1000, Rusty Russell wrote:
> On Wednesday 13 August 2008 17:06:03 Fernando Luis Vázquez Cao wrote:
> > Besides, I guess that accessing the io context information (such as
> > ioprio) of a request through elevator-specific private structures is not
> > something we want virtio_blk (or future users) to do.
> 
> The only semantic I assumed was "higher is better".  The server (ie. host) can 
> really only use the information to schedule between I/Os for that particular 
> guest anyway.
> 
> But it sounds like I should be passing "0" in there unconditionally until the 
> kernel semantics are sorted out and I can do something more intelligent?  I 
> haven't checked, but I assume that's actually what's happening at the moment 
> (the field is zero)?
Yes, with the current implementation the field is always zero, but
things might change. Instead of passing 0 unconditionally I think we
could use a function that extracts/calculates the ioprio of requests.
The patch I sent you yesterday is the first step in that direction. Is
this a valid approach for you?

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