This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] Re: [PATCH] xen: always handle VIRQ_TIMER first.

To: "Jeremy Fitzhardinge" <jeremy@xxxxxxxx>, "Keir Fraser" <keir@xxxxxxx>
Subject: Re: [Xen-devel] Re: [PATCH] xen: always handle VIRQ_TIMER first.
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Mon, 18 Oct 2010 14:20:14 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Campbell <ian.campbell@xxxxxxxxxx>
Delivery-date: Mon, 18 Oct 2010 06:21:25 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4CBA937C.6060301@xxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <C8DF0F4F.262B3%keir@xxxxxxx> <4CBA937C.6060301@xxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>>> On 17.10.10 at 08:11, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
> I think (but I haven't spelunked into that code lately) that after a
> tickless idle period it will update jiffies N ticks based on the
> clocksource, and then run any other interrupt handler code, so jiffies
> will always appear to be up to date.
> Ah, yes, here it is:
> /**
>  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
>  *
>  * Called from interrupt entry when the CPU was idle
>  *
>  * In case the sched_tick was stopped on this CPU, we have to check if 
> jiffies
>  * must be updated. Otherwise an interrupt handler could use a stale jiffy
>  * value. We do this unconditionally on any cpu, as we don't know whether 
> the
>  * cpu, which has the update task assigned is in a long sleep.
>  */
> static void tick_nohz_update_jiffies(ktime_t now)
> {
>       ...
> }

But this is available only with CONFIG_NO_HZ, which is a freely
selectable option. So perhaps the code should still be added
inside an #ifndef CONFIG_NO_HZ?


Xen-devel mailing list