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

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Message-ID: <49B6B9D2.8000807@freescale.com>
Date:	Tue, 10 Mar 2009 14:04:50 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	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()

Grant Likely wrote:

> I typically use something in the form of this pattern on powerpc code
> when I absolutely have to busywait.
>     int end_ts = get_tbl() + some_delay;  /* note that this is signed */
>     while (end_ts - get_tbl() > 0)
>         if (condition)
>             break;

Funny you mention this, because I was just about to implement the same
thing.  Of course, it will be a PowerPC-only function, but I suppose
that's its fate regardless.

> This macro also looks like a tempting unbounded latency tarpit to fall
> into when people start using it in critical regions,  but that goes
> for code using a non-timed-out busywait also.

I can't fix everything!

-- 
Timur Tabi
Linux kernel developer at Freescale
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