WARNING - OLD ARCHIVES

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/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] [PATCH] Avoid endless loop for vcpu migration

To: Keir Fraser <keir.xen@xxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Avoid endless loop for vcpu migration
From: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Date: Tue, 15 Mar 2011 11:29:29 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Jan Beulich <JBeulich@xxxxxxxxxx>
Delivery-date: Tue, 15 Mar 2011 03:30:12 -0700
Dkim-signature: v=1; a=rsa-sha256; c=simple/simple; d=ts.fujitsu.com; i=juergen.gross@xxxxxxxxxxxxxx; q=dns/txt; s=s1536b; t=1300184973; x=1331720973; h=message-id:date:from:mime-version:to:cc:subject: references:in-reply-to:content-transfer-encoding; bh=NOdwgc0ninkEn4GWwpsF8+pr6bTjBNHywVHHZkvzffI=; b=ihDWLwW3wdwiEs+REAWjOiG3MUzNzAGZ6lLemMmYGDc6glSsMDdlaz9n qdEp5LbX5hWFHP+VMB51rp888aw369/sENLOO/iAvc1X4gp6BM7E9Z1lj EGq5v0EClPonW/87xsY1+5f+sJoXG30nmN9AV6azb5We8ecprOPDtX5ot 14ee2cAHOOzT/acncjxj6M0PffAPLE1h/oDzzF9BJzoViV7XTPbL2ZF84 y+gE74J8aIZvlUZVUeesetujNvpL4;
Domainkey-signature: s=s1536a; d=ts.fujitsu.com; c=nofws; q=dns; h=X-SBRSScore:X-IronPort-AV:Received:X-IronPort-AV: Received:Received:Message-ID:Date:From:Organization: User-Agent:MIME-Version:To:CC:Subject:References: In-Reply-To:Content-Type:Content-Transfer-Encoding; b=RQXhbF61t1EdUixlEcefKWJ6q8UPTZcoHKvPtYbpUaa3lqL4ImtnEPBy Z6aVdac5G3+zOB0fUeFYo5com1zQ3lsn3ykvWktAlvpGoB/P1ZYW16Ift NDsioOl3PAL/BogjUGJWQ8TtU6nIvrD0OFR/m3WKQw9mcdhkw0Oma6wQ/ C2xFGdCRpv0OU9elTYMcKuE+l+hWp3d4Gp53dWhppcDYqqv4cbdlEndR0 3wvPjsDbwV9+ENuGcElwSOMkBgAKw;
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <C9A4E8CD.14CCE%keir.xen@xxxxxxxxx>
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>
Organization: Fujitsu Technology Solutions
References: <C9A4E8CD.14CCE%keir.xen@xxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20101226 Iceowl/1.0b1 Icedove/3.0.11
On 03/15/11 10:58, Keir Fraser wrote:
On 15/03/2011 09:21, "Juergen Gross"<juergen.gross@xxxxxxxxxxxxxx>  wrote:

That candidate-is-valid check seems absolutely independent of the
particular scheduler used, and hence could be done in the (sole)
caller, thus not requiring any change to the scheduler interface.

Which at once would eliminate unnecessary calls into pick_cpu (i.e.
you'd call it a second time only if the previously selected CPU really
is no longer valid to be used for that vCPU).

True.

The patch seems to become smaller :-)

By the way, why is the cpu_isset(new_cpu, v->domain->vcpupool->cpu_valid)
check required (after calling pick_cpu, in the cuirrently checked-in code)?

Good question. It shouldn't be required, as pick_cpu should check this and
should return only cpus in the current cpupool. With the latest patches from
Jan this seems to be true. :-)
I think I'll send a separate patch to remove the check.

You already check that pick_cpu was called holding the correct pair of
locks, if it has returned a cpu that is not in the pool's cpu_valid mask,
what would make pick_cpu return anything different on the next invocation
thus avoiding an endless loop?

Nothing. If pick_cpu is returning a cpu outside of it's cpupool, the loop
could be infinite. Inserting a BUG_ON would be a good idea, but this would
require a bit more logic, as a cpu might be removed from the cpupool during
a running vcpu_migrate (this case is handled by the call of
cpu_disable_scheduler() during removing a cpu from a cpupool).


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
TSP ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
Fujitsu Technology Solutions              e-mail: juergen.gross@xxxxxxxxxxxxxx
Domagkstr. 28                           Internet: ts.fujitsu.com
D-80807 Muenchen                 Company details: ts.fujitsu.com/imprint.html

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel