From: George Dunlap <george.dunlap@citrix.com>
To: Dario Faggioli <dario.faggioli@citrix.com>,
xen-devel@lists.xenproject.org
Cc: Juergen Gross <jgross@suse.com>, Jan Beulich <jbeulich@suse.com>
Subject: Re: [PATCH v2 1/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP
Date: Mon, 27 Mar 2017 12:49:32 +0100 [thread overview]
Message-ID: <67b9d187-7ad0-6a51-2305-12ae6dae0cfe@citrix.com> (raw)
In-Reply-To: <148977477739.22479.7043154591081622447.stgit@Palanthas.fritz.box>
On 17/03/17 18:19, Dario Faggioli wrote:
> Within context_saved(), we call the context_saved hook,
> and we use VCPU2OP() to determine from what scheduler.
> VCPU2OP uses DOM2OP, which uses d->cpupool, which is
> NULL when d is the idle domain. And in that case,
> DOM2OP just returns ops, the scheduler of cpupool0.
>
> Therefore, if:
> - cpupool0's scheduler defines context_saved (like
> Credit2 and RTDS do),
> - we are not in cpupool0 (i.e., our scheduler is
> not ops),
> - we are context switching from idle,
>
> we call VCPU2OP(idle_vcpu), which means
> DOM2OP(idle->cpupool), which is ops.
>
> Therefore, we both:
> - check if context_saved is defined in the wrong
> scheduler;
> - if yes, call the wrong one.
>
> When using Credit2 at boot, and also Credit2 in
> the other cpupool, this is wrong but innocuous,
> because it only involves the idle vcpus.
>
> When using Credit2 at boot, and Credit1 in the
> other cpupool, this is *totally* wrong, and
> it's by chance it does not explode!
>
> When using Credit2 and other schedulers I'm
> developping, I hit the following assert (in
> sched_credit2.c, on a CPU inside a cpupool that
> does not use Credit2):
>
> csched2_context_saved()
> {
> ...
> ASSERT(!vcpu_on_runq(svc));
> ...
> }
>
> Fix this by dealing explicitly, in VCPU2OP, with
> idle vcpus, returning the scheduler of the pCPU
> they (always) run on.
>
> While there, rename VCPU2OP itself to something
> that makes it easier to understand what it does.
This seems to have been moved into patch 2/2 -- I'll remove this
paragraph on commit if that's OK with you.
-George
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next prev parent reply other threads:[~2017-03-27 11:49 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-17 18:19 [PATCH v2 0/2] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP Dario Faggioli
2017-03-17 18:19 ` [PATCH v2 1/2] " Dario Faggioli
2017-03-17 18:27 ` Juergen Gross
2017-03-17 18:29 ` Juergen Gross
2017-03-20 8:01 ` Jan Beulich
2017-03-27 11:48 ` George Dunlap
2017-03-27 11:49 ` George Dunlap [this message]
2017-03-27 15:07 ` Dario Faggioli
2017-03-17 18:19 ` [PATCH v2 2/2] xen: sched: improve robustness (and rename) DOM2OP() Dario Faggioli
2017-03-27 13:23 ` George Dunlap
2017-03-27 15:13 ` Dario Faggioli
2017-04-06 10:59 ` Dario Faggioli
2017-04-06 11:06 ` Juergen Gross
2017-04-07 0:31 ` Dario Faggioli
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