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

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Date:	Wed, 11 Mar 2009 16:58:06 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Timur Tabi <timur@...escale.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	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()

> Are you talking about the udelay() inside the loop?  If so, I agree
> that this is bad and have removed it in the PowerPC-specific version:

The behaviour you want there is system specific - 10uS is a minimum
politeness value for x86 PCI bus for example.

> rdtsc instruction.  In this case, we're not adding arbitrary delays
> into the loop, and we're not using jiffies, but we are
> architecture-dependent.

and not useful

A macro of this form really needs to be able to look like

	spin_until_timeout(readb(foo) & 0x80, 30 * HZ) {
		udelay(10);
		/* Maybe do other stuff */
	}

to be more generally useful
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