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Re: [Xen-devel] [PATCH v2] xen: sched_credit: filter node-affinity mask against online cpus
On 17/09/13 16:16, Dario Faggioli wrote:
in _csched_cpu_pick(), as not doing so may result in the domain's
node-affinity mask (as retrieved by csched_balance_cpumask() )
and online mask (as retrieved by cpupool_scheduler_cpumask() )
having an empty intersection.
Therefore, when attempting a node-affinity load balancing step
and running this:
...
/* Pick an online CPU from the proper affinity mask */
csched_balance_cpumask(vc, balance_step, &cpus);
cpumask_and(&cpus, &cpus, online);
...
we end up with an empty cpumask (in cpus). At this point, in
the following code:
....
/* If present, prefer vc's current processor */
cpu = cpumask_test_cpu(vc->processor, &cpus)
? vc->processor
: cpumask_cycle(vc->processor, &cpus);
....
an ASSERT (from inside cpumask_cycle() ) triggers like this:
(XEN) Xen call trace:
(XEN) [<ffff82d08011b124>] _csched_cpu_pick+0x1d2/0x652
(XEN) [<ffff82d08011b5b2>] csched_cpu_pick+0xe/0x10
(XEN) [<ffff82d0801232de>] vcpu_migrate+0x167/0x31e
(XEN) [<ffff82d0801238cc>] cpu_disable_scheduler+0x1c8/0x287
(XEN) [<ffff82d080101b3f>] cpupool_unassign_cpu_helper+0x20/0xb4
(XEN) [<ffff82d08010544f>] continue_hypercall_tasklet_handler+0x4a/0xb1
(XEN) [<ffff82d080127793>] do_tasklet_work+0x78/0xab
(XEN) [<ffff82d080127a70>] do_tasklet+0x5f/0x8b
(XEN) [<ffff82d080158985>] idle_loop+0x57/0x5e
(XEN)
(XEN)
(XEN) ****************************************
(XEN) Panic on CPU 1:
(XEN) Assertion 'cpu < nr_cpu_ids' failed at
/home/dario/Sources/xen/xen/xen.git/xen/include/xe:16481
It is for example sufficient to have a domain with node-affinity
to NUMA node 1 running, and issueing a `xl cpupool-numa-split'
would make the above happen. That is because, by default, all
the existing domains remain assigned to the first cpupool, and
it now (after the cpupool-numa-split) only includes NUMA node 0.
This change prevents that by generalizing the function used
for figuring out whether a node-affinity load balancing step
is legit or not. This way we can, in _csched_cpu_pick(),
figure out early enough that the mask would end up empty,
skip the step all together and avoid the splat.
Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
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