Re: [Xen-devel] [PATCH 0/3] xen/sched: use new idle scheduler for free cpus

From: Dario Faggioli <dfaggioli@suse.com>
To: Juergen Gross <JGross@suse.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "sstabellini@kernel.org" <sstabellini@kernel.org>,
	"wl@xen.org" <wl@xen.org>,
	"konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
	"George.Dunlap@eu.citrix.com" <George.Dunlap@eu.citrix.com>,
	"ian.jackson@eu.citrix.com" <ian.jackson@eu.citrix.com>,
	"tim@xen.org" <tim@xen.org>,
	"julien.grall@arm.com" <julien.grall@arm.com>,
	Jan Beulich <JBeulich@suse.com>,
	"andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>
Subject: Re: [Xen-devel] [PATCH 0/3] xen/sched: use new idle scheduler for free cpus
Date: Tue, 13 Aug 2019 15:51:04 +0000	[thread overview]
Message-ID: <b763c05de403033802e28cee5854e86aadf3dc1f.camel@suse.com> (raw)
In-Reply-To: <20190802130730.15942-1-jgross@suse.com>

[-- Attachment #1.1: Type: text/plain, Size: 1798 bytes --]

On Fri, 2019-08-02 at 15:07 +0200, Juergen Gross wrote:
> These three patches have been carved out from my core scheduling
> series
> as they are sufficiently independent to be applied even without the
> big
> series.
> 
> Without this little series there are messages like the following to
> be
> seen on the console when booting with smt=0:
> 
> (XEN) Adding cpu 1 to runqueue 0
> (XEN) CPU 1 still not dead...
> (XEN) CPU 1 still not dead...
> (XEN) CPU 1 still not dead...
> (XEN) CPU 1 still not dead...
> 
> By assigning cpus to Cpupool-0 only after all cpus are up and by not
> using the more complicated credit2 scheduler for cpus not in any
> cpupool this situation can simply no longer happen, as parking the
> not
> to be started threads is done before.
> 
And this is not the only problem, solved by this series (or an
equivalent approach).

Right now, CPUs that are not in any pool, still belong to Pool-0's
scheduler. This forces us to make, within the scheduler, extra effort
to avoid actually running vCPUs on those.

In the case of Credit1, this also cause issue to weights
(re)distribution, as the number of CPUs available to the scheduler is
wrong.

So, we absolutely want something like this.

This is described in the changelog of commit e7191920261d ("xen:
credit2: never consider CPUs outside of our cpupool").

Would it be possible to mention this in one of the changelogs of the
series (patch 3 would be the best place, I think).

Thanks and Regards,
Dario
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
-------------------------------------------------------------------
<<This happens because _I_ choose it to happen!>> (Raistlin Majere)

[-- Attachment #1.2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

[-- Attachment #2: Type: text/plain, Size: 157 bytes --]

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel