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Date: Tue, 10 Mar 2009 16:05:20 +0000
Message-ID: <87a5b0800903100905l71f15141n7a273df21bfa77e2@mail.gmail.com>
Subject: Re: [PATCH v4] introduce macro spin_event_timeout()
From: Will Newton <will.newton@gmail.com>
To: Timur Tabi <timur@freescale.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org,
       rdreier@cisco.com, jirislaby@gmail.com, peterz@infradead.org,
       hancockrwd@gmail.com, jeremy@goop.org
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On Tue, Mar 10, 2009 at 3:50 PM, Timur Tabi <timur@freescale.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.