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

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Date:	Fri, 13 Mar 2009 14:03:41 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Timur Tabi <timur@...escale.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	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()


> 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().

I think that's where you're wrong :-)

Just require the delay inside the loop, it will make everything nicer.
There are also some good reasons to do that:

 - The delay between "polls" of the register may have to be controlled,
for example some HW will choke if polled too fast

 - If you aren't in an atomic section, you may want to use msleep() and
thus be schedule friendly

 - It fixes all the problems mentioned earlier

Cheers,
Ben.

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