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

[Justin Weaver <jtweaver@xxxxxxxxxx>]

On Mon, Feb 2, 2015 at 4:24 AM, Dario Faggioli
<dario.faggioli@xxxxxxxxxx> wrote:
> 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).

Dario,

Please see attached draft v2 1/2 patch.

Changes since v1:
 * Added dynamically allocated cpumasks to avoid putting them on the stack
 * Added helper function for code suggested in v1 review and called in two
   locations in function choose_cpu
 * Replaced two instances of cpumask_and/cpumask_empty with cpumask_intersects
 * Removed coding style fix in function balance_load
 * Improved comment in function runq_candidate
Debugging changes:
* During an affinity change, migrate only gets called when the current
and destination run queues are different
* The changes to schedule.c and domctl.c are only for debugging
(printk calls that only trigger during an affinity change)

Thank you,
Justin

Attachment: sched-credit2-v2_1of2_draft.patch
Description: Binary data

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