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

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Message-ID: <87a5b0800903100905l71f15141n7a273df21bfa77e2@mail.gmail.com>
Date:	Tue, 10 Mar 2009 16:05:20 +0000
From:	Will Newton <will.newton@...il.com>
To:	Timur Tabi <timur@...escale.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org,
	rdreier@...co.com, jirislaby@...il.com, peterz@...radead.org,
	hancockrwd@...il.com, jeremy@...p.org
Subject: Re: [PATCH v4] introduce macro spin_event_timeout()

On Tue, Mar 10, 2009 at 3:50 PM, Timur Tabi <timur@...escale.com> wrote:
> Alan Cox wrote:
>
>> NAK this - on a lot of platforms 1uS is the wrong timescale. Also we
>> shouldn't be encouraging this kind of polling by making it very easy to
>> write.
>
> Well, I can agree that the time scale might be wrong on some platforms.
>  The original version of spin_event_timeout() used jiffies, but some
> people said that a jiffy is too long of a timescale, so I changed it to
> udelay.

The correct timescale is rather application dependant - for some
accesses that cross clock domains it can be a requirement to wait for
a small number of core clock cycles (2 - 20) for a condition to become
true, for others, e.g. PIO, it is more appropriate to wait for a few
100 cycles.
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