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Date: Wed, 11 Mar 2009 15:45:47 -0500
Message-ID: <ed82fe3e0903111345m2962f5b5wdfc9e2efae1c33ae@mail.gmail.com>
Subject: Re: [PATCH v5] introduce macro spin_event_timeout()
From: Timur Tabi <timur@freescale.com>
To: Scott Wood <scottwood@freescale.com>
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Cc: linuxppc-dev@ozlabs.org, Roland Dreier <rdreier@cisco.com>
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On Wed, Mar 11, 2009 at 2:22 PM, Scott Wood <scottwood@freescale.com> wrote=
:

> I was under the impression that we were only talking about timeouts, and
> that the common case was significantly shorter than that.

I think one of the concerns that Alan Cox raised is that the existence
of this macro would encourage people to spin for long durations.

> If it's atomic because preemption was disabled, yes -- but even a rare
> extended spin in such a context would be bad for hard realtime. =A0If
> interrupts are disabled, or the code is executing from a timer interrupt =
(or
> possibly other interrupts depending on the hardware and its priority
> scheme), no.

So in that case, I can't rely on jiffies.  I guess get_cycle() is my
only choice.  The problem is that there is no num_cycles_per_usec().

--=20
Timur Tabi
Linux kernel developer at Freescale