linux-kernel - Re: [PATCH] port jRCU from 3.3 to 3.4

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Message-ID: <20120522152404.GW27374@one.firstfloor.org>
Date:	Tue, 22 May 2012 17:24:04 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Joe Korty <joe.korty@...r.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"stasn77@...il.com" <stasn77@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] port jRCU from 3.3 to 3.4

On Tue, May 22, 2012 at 09:38:58AM -0400, Joe Korty wrote:
> On Mon, May 21, 2012 at 06:57:44PM -0400, Andi Kleen wrote:
> > Joe Korty <joe.korty@...r.com> writes:
> > > + *
> > > + * jRCU assumes that the frames are large enough that architecture barrier
> > > + * operations performed in one frame have fully completed by the start of
> > > + * the next.  This period is presumed to be in the tens of microseconds, so
> > > + * it may not be wise to run jRCU at a frame rate under 100 usecs.
> > 
> > This sounds like a very dangerous assumption.
> 
> Yeah, I may have to go to a spin lock.  Easy to do, but
> I didn't want the serialization that results.  I figured
> that with a frame rate of 20 - 1000 Hz it wasn't necessary.

I think you have to. Relying on timing like this is just a ticking
time bomb.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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