Subject: Re: request->ioprio
From: Fernando Luis =?ISO-8859-1?Q?V=E1zquez?= Cao 
	<fernando@oss.ntt.co.jp>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jens Axboe <jens.axboe@oracle.com>, linux-kernel@vger.kernel.org,
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	<yoshikawa.takuya@oss.ntt.co.jp>,
       dpshah@google.com
In-Reply-To: <200808141216.33688.rusty@rustcorp.com.au>
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	 <200808070633.06112.rusty@rustcorp.com.au>
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	 <200808141216.33688.rusty@rustcorp.com.au>
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Organization: NTT Open Source Software Center
Date: Thu, 14 Aug 2008 13:26:46 +0900
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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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