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

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Date:	Thu, 12 Mar 2009 11:19:57 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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:

> #define spin_until_timeout(condition, timeout, rc)          \
>       for (unsigned long __timeout = jiffies + (timeout);     \
>               (!(rc = (condition)) && time_after(jiffies, __timeout)); )

Ooo, that's good.

I'm still not crazy about using jiffies, since it doesn't get
incremented when interrupts are disabled, and I'd like this function to
work in those cases.  How about get_cycles()?  I know it's not supported
on all platforms, but I'm willing to live with that.

The other problem with get_cycles() is that there doesn't appear to be a
num_cycles_per_usec() function, so there's no way for me to scale the
count to a fixed time period.

-- 
Timur Tabi
Linux kernel developer at Freescale
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