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

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Message-ID: <ed82fe3e0903121205k552a83bft9ac3b63c64a293c8@mail.gmail.com>
Date:	Thu, 12 Mar 2009 14:05:05 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, rdreier@...co.com,
	jirislaby@...il.com, will.newton@...il.com, hancockrwd@...il.com,
	jeremy@...p.org
Subject: Re: [PATCH v4] introduce macro spin_event_timeout()

On Thu, Mar 12, 2009 at 11:50 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> sched_clock() does that, but:
>  - it falls back to jiffies on poor platforms

I think it's ok to fall back to jiffies where necessary, but these two
functions are too heavy-weight for my tastes.

> But something that seems to always work, is simply count loops and rely
> on whatever delay is in the specified loop.
>
> #define spin_until_timeout(condition, timeout, rc) \
>        for (unsigned long __timeout = 0; \
>             !(rc = (condition)) && __timeout < (timeout); \
>             __timeout++)

But that's the thing - I don't want a required delay inside the loop.

I guess I'm going to have to think about this for a while.  I'd like
to see something like cycles_per_usec() as a companion function to
get_cycles().

-- 
Timur Tabi
Linux kernel developer at Freescale
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