linux-kernel - Re: [PATCH v4] introduce macro spin_event

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Date:	Wed, 11 Mar 2009 20:45:57 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Timur Tabi <timur@...escale.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, rdreier@...co.com,
	jirislaby@...il.com, peterz@...radead.org, will.newton@...il.com,
	hancockrwd@...il.com, jeremy@...p.org
Subject: Re: [PATCH v4] introduce macro spin_event_timeout()

On Wed, Mar 11, 2009 at 3:58 PM, Benjamin Herrenschmidt
<benh@...nel.crashing.org> wrote:
> On Wed, 2009-03-11 at 13:18 -0500, Timur Tabi wrote:
>> Alan Cox wrote:
>> >> Are you talking about the udelay() inside the loop?  If so, I agree
>> >> that this is bad and have removed it in the PowerPC-specific version:
>> >
>> > The behaviour you want there is system specific - 10uS is a minimum
>> > politeness value for x86 PCI bus for example.
>>
>> So we need to allow for delays between successive rights?  We can
>> provide that with a third parameter to the macro.
>
> I prefer Alan's method of having the macro be followed by { and } so we
> can add things in there. The delay between access will often be somewhat
> platform or device specific, and some drivers might be able to do useful
> things while spinning.
>
> The other big advantage of that approach is that drivers that aren't in
> an atomic section can use msleep() and allow the kernel to schedule on
> that processor.

Ack!  I totally agree.

g.


-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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