[Xen-devel] [PATCH v2] xen/sched: fix onlining cpu with core scheduling active

[Xen-devel] [PATCH v2] xen/sched: fix onlining cpu with core scheduling active

[Juergen Gross]

When onlining a cpu cpupool_cpu_add() checks whether all siblings of
the new cpu are free in order to decide whether to add it to cpupool0.
In case the added cpu is not the last sibling to be onlined this test
is wrong as it only checks for all online siblings to be free. The
test should include the check for the number of siblings having
reached the scheduling granularity of cpupool0, too.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V2:
- modify condition form >= to == (Jan Beulich)
---
 xen/common/sched/cpupool.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/common/sched/cpupool.c b/xen/common/sched/cpupool.c
index 9f70c7ec17..d40345b585 100644
--- a/xen/common/sched/cpupool.c
+++ b/xen/common/sched/cpupool.c
@@ -616,7 +616,8 @@ static int cpupool_cpu_add(unsigned int cpu)
     get_sched_res(cpu)->cpupool = NULL;
 
     cpus = sched_get_opt_cpumask(cpupool0->gran, cpu);
-    if ( cpumask_subset(cpus, &cpupool_free_cpus) )
+    if ( cpumask_subset(cpus, &cpupool_free_cpus) &&
+         cpumask_weight(cpus) == cpupool_get_granularity(cpupool0) )
         ret = cpupool_assign_cpu_locked(cpupool0, cpu);
 
     rcu_read_unlock(&sched_res_rculock);
-- 
2.16.4


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Re: [Xen-devel] [PATCH v2] xen/sched: fix onlining cpu with core scheduling active

[Jürgen Groß]

Ping?

On 10.03.20 10:06, Juergen Gross wrote:
> When onlining a cpu cpupool_cpu_add() checks whether all siblings of
> the new cpu are free in order to decide whether to add it to cpupool0.
> In case the added cpu is not the last sibling to be onlined this test
> is wrong as it only checks for all online siblings to be free. The
> test should include the check for the number of siblings having
> reached the scheduling granularity of cpupool0, too.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
> V2:
> - modify condition form >= to == (Jan Beulich)
> ---
>   xen/common/sched/cpupool.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/common/sched/cpupool.c b/xen/common/sched/cpupool.c
> index 9f70c7ec17..d40345b585 100644
> --- a/xen/common/sched/cpupool.c
> +++ b/xen/common/sched/cpupool.c
> @@ -616,7 +616,8 @@ static int cpupool_cpu_add(unsigned int cpu)
>       get_sched_res(cpu)->cpupool = NULL;
>   
>       cpus = sched_get_opt_cpumask(cpupool0->gran, cpu);
> -    if ( cpumask_subset(cpus, &cpupool_free_cpus) )
> +    if ( cpumask_subset(cpus, &cpupool_free_cpus) &&
> +         cpumask_weight(cpus) == cpupool_get_granularity(cpupool0) )
>           ret = cpupool_assign_cpu_locked(cpupool0, cpu);
>   
>       rcu_read_unlock(&sched_res_rculock);
> 

Re: [Xen-devel] [PATCH v2] xen/sched: fix onlining cpu with core scheduling active

[Dario Faggioli]

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On Tue, 2020-03-10 at 10:06 +0100, Juergen Gross wrote:
> When onlining a cpu cpupool_cpu_add() checks whether all siblings of
> the new cpu are free in order to decide whether to add it to
> cpupool0.
> In case the added cpu is not the last sibling to be onlined this test
> is wrong as it only checks for all online siblings to be free. The
> test should include the check for the number of siblings having
> reached the scheduling granularity of cpupool0, too.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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