linux-kernel - Re: [PATCH v3] add function spin_event

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Date:	Mon, 09 Mar 2009 15:54:19 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Jiri Slaby <jirislaby@...il.com>
CC:	linux-kernel@...r.kernel.org, rdreier@...co.com,
	peterz@...radead.org, will.newton@...il.com
Subject: Re: [PATCH v3] add function spin_event_timeout()

Jiri Slaby wrote:
> On 9.3.2009 21:32, Timur Tabi wrote:
>> +#define spin_event_timeout(condition, timeout)				\
>> +({									\
>> +	int __timeout = timeout;					\
>> +	while (!(condition)&&  --__timeout) {				\
>> +		udelay(1);						\
>> +		cpu_relax();						\
> 
> So you don't need cpu_relax anymore...

I checked the udelay() code.  It varies per platform, but I didn't see
how it always replicated the functionality of cpu_relax().  For example,
in x86_64, cpu_relax is a "rep; nop;".  But I don't see that code
sequence in arch/x86/lib/delay.c.

So I presume that something in the delay functions makes cpu_relax()
unnecessary.  What exactly is the purpose of cpu_relax()?

> And I would make timeout UL like delay functions.

I made it an integer because I don't expect anyone to pass a value
larger than 2^31, but I'll change it.

-- 
Timur Tabi
Linux kernel developer at Freescale
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