Re: [PATCH 1/2] xen: export do_yield as vcpu_yield

[George Dunlap <george.dunlap@eu.citrix.com>]

On 07/23/2014 01:05 PM, Stefano Stabellini wrote:
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> CC: george.dunlap@eu.citrix.com
> CC: JBeulich@suse.com
> ---
>   xen/common/schedule.c   |   10 +++++-----
>   xen/include/xen/sched.h |    1 +
>   2 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/xen/common/schedule.c b/xen/common/schedule.c
> index e9eb0bc..6631dc8 100644
> --- a/xen/common/schedule.c
> +++ b/xen/common/schedule.c
> @@ -795,9 +795,8 @@ static long do_poll(struct sched_poll *sched_poll)
>   }
>   
>   /* Voluntarily yield the processor for this allocation. */
> -static long do_yield(void)
> +void vcpu_yield(struct vcpu *v)

What are you actually trying to do here?  Why do you add a vcpu struct, 
when all the callers (including the one you add in 2/2) just pass current?

>   {
> -    struct vcpu * v=current;
>       spinlock_t *lock = vcpu_schedule_lock_irq(v);
>   
>       SCHED_OP(VCPU2OP(v), yield, v);
> @@ -805,7 +804,6 @@ static long do_yield(void)
>   
>       TRACE_2D(TRC_SCHED_YIELD, current->domain->domain_id, current->vcpu_id);
>       raise_softirq(SCHEDULE_SOFTIRQ);

This is broken: it's still tracing current instead of v, and you're 
raising the schedule softirq on the current cpu rather than on the cpu 
on which v is running.  If v!=current, you have to go through force 
reschedule for safety.

Just rename the function and make it non-static, leaving the arguments 
and return value alone.

  -George