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Re: [Xen-merge] Re: [patch] SMP alternatives for i386

To: Zwane Mwaikambo <zwane@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-merge] Re: [patch] SMP alternatives for i386
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Wed, 14 Dec 2005 20:15:01 +0000
Cc: Gerd Knorr <kraxel@xxxxxxx>, Xen merge mainline list <xen-merge@xxxxxxxxxxxxxxxxxxx>, linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx>
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On 14 Dec 2005, at 19:35, Zwane Mwaikambo wrote:

diff -urN -x 'build-*' -x '*~' -x Make -x scripts linux-2.6.15-rc5/arch/i386/kernel/smpboot.c work-2.6.15-rc5/arch/i386/kernel/smpboot.c --- linux-2.6.15-rc5/arch/i386/kernel/smpboot.c 2005-12-06 17:00:36.000000000 +0100 +++ work-2.6.15-rc5/arch/i386/kernel/smpboot.c 2005-12-06 17:06:48.000000000 +0100
@@ -1351,6 +1352,9 @@
        fixup_irqs(map);
        /* It's now safe to remove this processor from the online map */
        cpu_clear(cpu, cpu_online_map);
+
+       if (1 == num_online_cpus())
+               alternatives_smp_switch(0);
        return 0;
 }

Is that really safe there? Ideally you want to do the switch when the
processor going offline is no longer executing kernel code.

Perhaps that check belongs at the end of __cpu_die()? That's where it lives in xen's smpboot.c.

 -- Keir


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