linux-kernel - Re: request->ioprio

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Message-Id: <200808161713.37146.rusty@rustcorp.com.au>
Date:	Sat, 16 Aug 2008 17:13:36 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Fernando Luis Vázquez Cao 
	<fernando@....ntt.co.jp>
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 Friday 15 August 2008 15:51:02 Fernando Luis Vázquez Cao wrote:
> 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.
>
> Does that mean you are not going to incorporate the prio class system
> that is used in Linux?

Actually, since it's unused at the moment, we can define it however we want.  
But note that this is an ABI; while the kernel-internal definitions are 
fluid, this semantic must stay the same (even if the actual values differ).

So we should probably put an explicit mapping function there anyway.

Thanks,
Rusty.
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