From: Juergen Gross <jgross@suse.com>
To: Dario Faggioli <dario.faggioli@citrix.com>,
xen-devel@lists.xenproject.org
Cc: George Dunlap <george.dunlap@citrix.com>,
Jan Beulich <jbeulich@suse.com>
Subject: Re: [PATCH] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP
Date: Fri, 17 Mar 2017 06:28:17 +0100 [thread overview]
Message-ID: <791f6a11-6a3c-63e3-b9e8-0941aa3b1fee@suse.com> (raw)
In-Reply-To: <148969985491.18518.5789656764002800021.stgit@Palanthas.fritz.box>
On 16/03/17 22:30, 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 taking care, in VCPU2OP, of the case
> when the vcpu is an idle one.
>
> Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
... with or without the remark below addressed.
> ---
> Cc: George Dunlap <george.dunlap@citrix.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Jan Beulich <jbeulich@suse.com>
> ---
> Cc-ing Jan, as this should be backported at least to 4.8, but, IMO, as back as
> possible.
> ---
> xen/common/schedule.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/xen/common/schedule.c b/xen/common/schedule.c
> index 223a120..d12f346 100644
> --- a/xen/common/schedule.c
> +++ b/xen/common/schedule.c
> @@ -78,7 +78,19 @@ static struct scheduler __read_mostly ops;
> : (typeof((opsptr)->fn(opsptr, ##__VA_ARGS__)))0 )
>
> #define DOM2OP(_d) (((_d)->cpupool == NULL) ? &ops : ((_d)->cpupool->sched))
> -#define VCPU2OP(_v) (DOM2OP((_v)->domain))
> +static inline struct scheduler* VCPU2OP(const struct vcpu *v)
Rename, e.g. get_scheduler() ?
> +{
> + struct domain *d = v->domain;
> +
> + if ( likely(d->cpupool != NULL) )
> + return d->cpupool->sched;
> +
> + /* v->processor never changes for idle vcpus, so using it here is safe */
> + if ( likely(is_idle_domain(d)) )
> + return per_cpu(scheduler, v->processor);
> + else
> + return &ops;
> +}
> #define VCPU2ONLINE(_v) cpupool_domain_cpumask((_v)->domain)
>
> static inline void trace_runstate_change(struct vcpu *v, int new_state)
Juergen
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next prev parent reply other threads:[~2017-03-17 5:28 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-16 21:30 [PATCH] xen: sched: don't call hooks of the wrong scheduler via VCPU2OP Dario Faggioli
2017-03-17 5:28 ` Juergen Gross [this message]
2017-03-17 11:46 ` Dario Faggioli
2017-03-17 7:42 ` Jan Beulich
2017-03-17 12:22 ` Dario Faggioli
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