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Date: Sat, 28 Jun 2008 12:44:53 +0200
From: Pavel Machek <pavel@suse.cz>
To: Ingo Molnar <mingo@elte.hu>
Cc: Marin Mitov <mitov@issp.bas.bg>, LKML <linux-kernel@vger.kernel.org>,
       Steven Rostedt <rostedt@goodmis.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       linux-rt-users <linux-rt-users@vger.kernel.org>, akpm@osdl.org,
       Clark Williams <clark.williams@gmail.com>,
       Peter Zijlstra <peterz@infradead.org>,
       "Luis Claudio R. Goncalves" <lclaudio@uudg.org>,
       Gregory Haskins <ghaskins@novell.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andi Kleen <andi-suse@firstfloor.org>
Subject: Re: [PATCH][resubmit] x86: enable preemption in delay
Message-ID: <20080628104453.GC10872@ucw.cz>
References: <200805252108.25011.mitov@issp.bas.bg> <200806091911.21850.mitov@issp.bas.bg> <20080609161606.GA24841@elte.hu> <200806152058.17142.mitov@issp.bas.bg> <20080618075518.GD4135@elte.hu>
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On Wed 2008-06-18 09:55:18, Ingo Molnar wrote:
> 
> * Marin Mitov <mitov@issp.bas.bg> wrote:
> 
> > Why not something like that (do keep in mind I am not an expert :-):
> > 
> > static void delay_tsc(unsigned long loops)
> > {
> > 	get and store the mask of allowed cpus;
> > 	/*     prevent the migration   */
> > 	set the mask of allowed cpus to the current cpu only;
> > 	/*     is it possible? could it be guaranteed?    */
> > 	loop for the delay;
> > 	restore the old mask of allowed cpus;
> > }
> > 
> > You have got the idea. Could it be realized? Is it more expensive than 
> > the current realization? So, comments, please.
> 
> hm, changing/saving/restorig cpus_allowed is really considered a 'heavy' 
> operation compared to preempt_disable(). On a 4096 CPUs box cpus_allowed 
> is 4096 bits which is half a kilobyte ...

Time to RLE the bitmap? 

<runs>							Pavel

-- 
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