[PATCH] locking/pvqspinlock: Wait early if vcpu is preempted

[PATCH] locking/pvqspinlock: Wait early if vcpu is preempted

[Pan Xinhui]

If prev node is not in runnig state or its cpu is preempted, we need
wait early in pv_wait_node. After commit "sched/core: Introduce the
vcpu_is_preempted(cpu) interface" kernel has knowledge of one vcpu is
running or not. So lets use it.

Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
---
 kernel/locking/qspinlock_paravirt.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index e3b5520..48648dc 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -263,7 +263,8 @@ pv_wait_early(struct pv_node *prev, int loop)
 	if ((loop & PV_PREV_CHECK_MASK) != 0)
 		return false;
 
-	return READ_ONCE(prev->state) != vcpu_running;
+	return READ_ONCE(prev->state) != vcpu_running ||
+				vcpu_is_preempted(prev->cpu);
 }
 
 /*
-- 
2.4.11

Re: [PATCH] locking/pvqspinlock: Wait early if vcpu is preempted

[Ingo Molnar]

* Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> wrote:

> If prev node is not in runnig state or its cpu is preempted, we need
> wait early in pv_wait_node. After commit "sched/core: Introduce the
> vcpu_is_preempted(cpu) interface" kernel has knowledge of one vcpu is
> running or not. So lets use it.

That's not how we reference upstream commits. I had to search the git log the hard 
way to figure out that it's commit d9345c65eb79 ...

Also, once you look at that commit you'll see how sloppy the capitalization in 
your changelog is. I fixed that up for all the original commits in the hope of you 
learning from those mistakes - but that was last year and the experiment failed.

Thanks,

	Ingo

Re: [PATCH] locking/pvqspinlock: Wait early if vcpu is preempted

[Pan Xinhui]

在 2017/1/5 16:23, Ingo Molnar 写道:
>
> * Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> wrote:
>
>> If prev node is not in runnig state or its cpu is preempted, we need
>> wait early in pv_wait_node. After commit "sched/core: Introduce the
>> vcpu_is_preempted(cpu) interface" kernel has knowledge of one vcpu is
>> running or not. So lets use it.
>
> That's not how we reference upstream commits. I had to search the git log the hard
> way to figure out that it's commit d9345c65eb79 ...
>
hi, Ingo
	Sorry. Such stupid mistake will not happen next time.

> Also, once you look at that commit you'll see how sloppy the capitalization in
> your changelog is. I fixed that up for all the original commits in the hope of you
> learning from those mistakes - but that was last year and the experiment failed.
>
So sorry, I pay most attention on spelling of words. :(
Maybe I rely on the tools of ./scripts/checkpatch.pl too much.
I will rewrite the comments and resend this patch.

> Thanks,
>
> 	Ingo
>