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] [PATCH]Check the values of MAX_VIRT_CPUS and NR_CPUS for

To: Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] [PATCH]Check the values of MAX_VIRT_CPUS and NR_CPUS for SMP
From: Tristan Gingold <Tristan.Gingold@xxxxxxxx>
Date: Fri, 21 Apr 2006 09:10:07 +0200
Delivery-date: Fri, 21 Apr 2006 00:06:24 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <200604210131.k3L1VgNc009129@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
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/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <200604210131.k3L1VgNc009129@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: KMail/1.5
Le Vendredi 21 Avril 2006 03:31, Atsushi SAKAI a écrit :
> Hi, All
>   This is a patch for checking # of CPUs consistency.
> This patch compares the values of MAX_VIRT_CPU and NR_CPUS.
> The object of this patch is to avoid boot error for SMP case.
> Reason for the need of this patch
> When we were testing SMP system, Boot sequence was failed
> in the case of using BVT scheduler.
> Each CPU assumed to have idle_vcpu in scheduler.
> But these two values inconsistency makes the cpus which is not assigned
> idle_vcpu. This case is occurred MAX_VIRT_CPUS is less than # of Real CPU.
> (for example MAX_VIRT_CPUS = 4 and Real CPU = 8
> 4Real CPUs are not assigned to idle_vcpu)
> Currently, no check routine exists in scheduler for this problem.
> To solve this problem, I added check routine in xen/sched.h.
> Current situations
> This problem is currently solved in IA64 by CSET;9495 patch by
> expanding both CPUS value to 64.
> (Previously MAX_VIRT_CPUS = 8 and NR_CPUS = 4)
> #define MAX_VIRT_CPUS 64 in xen/include/public/arch-ia64.h
> and
> #define NR_CPUS       64 in xen/include/asm-ia64/config.h
> But the logical limit of the IA64 Max CPU is larger than 64.
> If someone change these values, some possibility make this error again.
> To avoid this problem, I believe this check code should be exists.
Please also note that this problem is currently worked around in xen/ia64:
   /* A vcpu is created for the idle domain on every physical cpu.
       Limit the number of cpus to the maximum number of vcpus.  */
    if (max_cpus > MAX_VIRT_CPUS)
        max_cpus = MAX_VIRT_CPUS;

Of course, the Keir method is better!


Xen-devel mailing list