linux-kernel - Re: [PATCH 2/3] generic-ipi: remove kmalloc()

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Date:	Wed, 18 Feb 2009 11:52:29 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Jens Axboe <jens.axboe@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 2/3] generic-ipi: remove kmalloc()

On Wed, 2009-02-18 at 16:01 +1030, Rusty Russell wrote:
> On Wednesday 18 February 2009 08:29:06 Peter Zijlstra wrote:
> > Remove the use of kmalloc() from the smp_call_function_*() calls.
> 
> This patch is actually quite nice.  Not sure it's correct, but it's neat :)

:-)

> One minor quibble:
> 
> > +			data = &per_cpu(csd_data, me);
> 
> "data = &__get_cpu_var(csd_data);" is slightly preferred.  A few less cycles.

Thanks, next version will include the below.

Index: linux-2.6/kernel/smp.c
===================================================================
--- linux-2.6.orig/kernel/smp.c
+++ linux-2.6/kernel/smp.c
@@ -325,7 +325,7 @@ int smp_call_function_single(int cpu, vo
 			 * will make sure the callee is done with the
 			 * data before a new caller will use it.
 			 */
-			data = &per_cpu(csd_data, me);
+			data = &__get_cpu_var(csd_data);
 			csd_lock(data);
 		} else {
 			data = &d;
@@ -413,7 +413,7 @@ void smp_call_function_many(const struct
 		return;
 	}
 
-	data = &per_cpu(cfd_data, me);
+	data = &__get_cpu_var(cfd_data);
 	csd_lock(&data->csd);
 
 	spin_lock_irqsave(&data->lock, flags);


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