From: Peter Zijlstra <peterz@infradead.org>
To: Joel Fernandes <joelaf@google.com>
Cc: "Rajendran, Jaishankar" <jaishankar.rajendran@intel.com>,
Dario Faggioli <dfaggioli@suse.com>,
Vineeth Pillai <vineethrp@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Mallikarjun Chegaraddi,
Raju" <raju.mallikarjun.chegaraddi@intel.com>
Subject: Re: Core Scheduling - Concurrent VMs
Date: Tue, 27 Jul 2021 11:54:38 +0200 [thread overview]
Message-ID: <YP/X3nSGBfkZ1/c3@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAJWu+oq98Yh4kknze7u6SOYZNw6hR5aFkj61aXbTV3JPq=7RNg@mail.gmail.com>
On Mon, Jul 26, 2021 at 11:57:21AM -0400, Joel Fernandes wrote:
> Hi,
> +Dario Faggioli and +Vineeth Pillai as well.
>
> On Mon, Jul 26, 2021 at 1:41 AM Rajendran, Jaishankar
> <jaishankar.rajendran@intel.com> wrote:
> >
> > Refer to the below experiments performed using Core Scheduling for Concurrent VMs and we found the benchmark scores executed in different VMs are
> > degrading after enablement of Core Scheduling. Both the host and guest are enabled with Core Scheduler
>
> Why are you running core scheduling within the guest? Only the host
> needs it and you tag vCPU threads in the host. Within the guest you
> don't need it (and it probably doesn't make sense unless you pin the
> vCPU threads to individual physical hardware threads).
Correct, in-guest core-scheduling only works if there's an in-guest
topology, which requires pinning vcpu threads and sacrificing a chicken
on the altar of qemu to get the right incantation such that the guest
actually receives the right topology.
Nested core scheduling hurts my head.
> I don't think these commands can really tell you that core scheduler
> is working or not. They are too coarse grained. You would need to look
> at it through ftrace scheduling events. Core scheduling will still
> allow differently tagged threads to use a core, it is just that it
> wont allow it simultaneously.
Right, you need tracing to verify it actually works, no real alternative
there.
prev parent reply other threads:[~2021-07-27 9:54 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-26 5:41 Core Scheduling - Concurrent VMs Rajendran, Jaishankar
2021-07-26 15:57 ` Joel Fernandes
2021-07-27 9:54 ` Peter Zijlstra [this message]
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