Re: [Xen-devel] [PATCH 1/2] sched: credit2: respect per-vcpu hard affinity

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Sat, 2015-01-31 at 20:51 -1000, Justin Weaver wrote:
> On Mon, Jan 19, 2015 at 9:21 PM, Justin Weaver <jtweaver@xxxxxxxxxx> wrote:
> > On Mon, Jan 12, 2015 at 8:05 AM, Dario Faggioli

> For example...
> I start a guest with one vcpu with hard affinity 8 - 15 and xl
> vcpu-list says it's running on pcpu 15
> I run xl vcpu-pin 1 0 8 to change it to hard affinity only with pcpu 8
> When it gets to vcpu_wake, it tests vcpu_runnable(v) which is false
> because _VPF_blocked is set, so it skips the call to
> SCHED_OP(VCPU2OP(v), wake, v); and so does not get a runq_tickle
> xl vcpu-list now shows --- for the state and I cannot console into it
> What I don't understand though is if I then enter xl vcpu-pin 1 0 15
> it reports that _VPF_blocked is NOT set, vcpu_wake calls credit2's
> wake, it gets a runq_tickle and everything is fine again
> Why did the value of the _VPF_blocked flag change after I entered xl
> vcpu-pin the second time?? I dove deep in the code and could not
> figure it out.
> 
As promised, I am having a look. As I recalled, affinity
setting/changing should not involve fiddling with _VPF_blocked, so there
should be something else going on.

This seems to me to be confirmed by the fact that you can make the
system working again via another call to 'vcpu-pin'.

I'm playing a little bit with your code, with and without the call to
migrate(), to try and see better what's happening. If you happen to have
an updated version of it, even if still work-in progress, and not ready
for being the actual v2, and you want to share it, so that I can try
that one, please go ahead (just attach it to your reply, it's for
debugging, so no necessary for it to be a proper submission).

I'll let you know if I find something interesting.

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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