The problem:
On -RT, an emulated LAPIC timer instances has the following path:
1) hard interrupt
2) ksoftirqd is scheduled
3) ksoftirqd wakes up vcpu thread
4) vcpu thread is scheduled
This extra context switch introduces unnecessary latency in the
LAPIC path for a KVM guest.
The solution:
Al
The problem:
On -RT, an emulated LAPIC timer instances has the following path:
1) hard interrupt
2) ksoftirqd is scheduled
3) ksoftirqd wakes up vcpu thread
4) vcpu thread is scheduled
This extra context switch introduces unnecessary latency in the
LAPIC path for a KVM guest.
The solution:
Al
The problem:
On -RT, an emulated LAPIC timer instances has the following path:
1) hard interrupt
2) ksoftirqd is scheduled
3) ksoftirqd wakes up vcpu thread
4) vcpu thread is scheduled
This extra context switch introduces unnecessary latency in the
LAPIC path for a KVM guest.
The solution:
Al
The problem:
On -RT, an emulated LAPIC timer instances has the following path:
1) hard interrupt
2) ksoftirqd is scheduled
3) ksoftirqd wakes up vcpu thread
4) vcpu thread is scheduled
This extra context switch introduces unnecessary latency in the
LAPIC path for a KVM guest.
The solution:
Al
On Wed, Feb 25, 2015 at 10:02:50PM +0100, Sebastian Andrzej Siewior wrote:
> >+static inline int swait_active(struct swait_queue_head *q)
> >+{
> >+return !list_empty(&q->task_list);
>
> In RT there was a smp_mb() which you dropped and I assume you had
> reasons for it.
Yeah, RT didn't have
On Fri, Aug 07, 2015 at 12:57:38PM +0200, Peter Zijlstra wrote:
> > >+void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait)
> > this one has no users the __ suggests that it is locked edition. Maybe
> > it is for the completions…
>
> Yeah, who knows, I certainly do not anymor
On Fri, Aug 07, 2015 at 01:14:15PM +0200, Peter Zijlstra wrote:
> On that, we cannot convert completions to swait. Because swait wake_all
> must not happen from IRQ context, and complete_all() typically is used
> from just that.
If swait queues aren't useable from IRQ context they will be fairly
u
On Fri, Aug 07, 2015 at 09:41:31AM -0700, Christoph Hellwig wrote:
> On Fri, Aug 07, 2015 at 01:14:15PM +0200, Peter Zijlstra wrote:
> > On that, we cannot convert completions to swait. Because swait wake_all
> > must not happen from IRQ context, and complete_all() typically is used
> > from just t
On Fri, Aug 07, 2015 at 06:45:26PM +0200, Peter Zijlstra wrote:
> Its just the swait_wake_all() that is not. The entire purpose of them
> was to have something that allows bounded execution (RT and all).
Still not sure i that might be a too big burden for mainline, but at
least it's not as severe.
On Fri, 7 Aug 2015, Peter Zijlstra wrote:
> On Fri, Aug 07, 2015 at 12:57:38PM +0200, Peter Zijlstra wrote:
>
> > > >+void __finish_swait(struct swait_queue_head *q, struct swait_queue
> > > >*wait)
>
> > > this one has no users the __ suggests that it is locked edition. Maybe
> > > it is for th
On 01/14/2015 12:12 PM, Marcelo Tosatti wrote:
> The problem:
>
> On -RT, an emulated LAPIC timer instances has the following path:
>
> 1) hard interrupt
> 2) ksoftirqd is scheduled
> 3) ksoftirqd wakes up vcpu thread
> 4) vcpu thread is scheduled
>
> This extra context switch introduces unneces
On Fri, 16 Jan 2015 11:48:46 -0500
Steven Rostedt wrote:
> > static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
> > {
> > - DEFINE_WAIT(wait);
> > + DEFINE_SWAITER(wait);
> >
> > - prepare_to_wait(&vc->wq, &wait, TASK_INTERRUPTIBLE);
> > + swait_prepare(&vc->wq, &wait, TASK_INT
On Fri, 16 Jan 2015 11:40:45 -0500
Marcelo Tosatti wrote:
> The problem:
>
> On -RT, an emulated LAPIC timer instances has the following path:
>
> 1) hard interrupt
> 2) ksoftirqd is scheduled
> 3) ksoftirqd wakes up vcpu thread
> 4) vcpu thread is scheduled
>
> This extra context switch intro
On Fri, Jan 16, 2015 at 11:48:46AM -0500, Steven Rostedt wrote:
> I notice everywhere you have a swait_wake_interruptible() but here. Is
> there a reason why?
>
> IIRC, Peter wants to make swait wakeup usage homogenous. That is, you
> either sleep in an interruptible state, or you don't. You can't
On Fri, Jan 16, 2015 at 11:48:46AM -0500, Steven Rostedt wrote:
> > @@ -971,8 +971,8 @@
> > kvm_mips_callbacks->queue_timer_int(vcpu);
> >
> > vcpu->arch.wait = 0;
> > - if (waitqueue_active(&vcpu->wq)) {
> > - wake_up_interruptible(&vcpu->wq);
> > + if (swaitqueue_active(&v
On Mon, Jan 19, 2015 at 12:41:00PM -0200, Marcelo Tosatti wrote:
> On Fri, Jan 16, 2015 at 11:48:46AM -0500, Steven Rostedt wrote:
> > > static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
> > > {
> > > - DEFINE_WAIT(wait);
> > > + DEFINE_SWAITER(wait);
> > >
> > > - prepare_to_wait(&vc->
On Tue, 20 Jan 2015 16:46:53 +1100
Paul Mackerras wrote:
> On Mon, Jan 19, 2015 at 12:41:00PM -0200, Marcelo Tosatti wrote:
> > On Fri, Jan 16, 2015 at 11:48:46AM -0500, Steven Rostedt wrote:
> > > > static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
> > > > {
> > > > - DEFINE_WAIT
On Tue, Jan 20, 2015 at 01:16:13PM -0500, Steven Rostedt wrote:
> I'm actually wondering if we should just nuke the _interruptible()
> version of swait. As it should only be all interruptible or all not
> interruptible, that the swait_wake() should just do the wake up
> regardless. In which case, s
* Peter Zijlstra | 2015-01-21 16:07:16 [+0100]:
>On Tue, Jan 20, 2015 at 01:16:13PM -0500, Steven Rostedt wrote:
>> I'm actually wondering if we should just nuke the _interruptible()
>> version of swait. As it should only be all interruptible or all not
>> interruptible, that the swait_wake() shou
On Tue, Feb 17, 2015 at 06:44:19PM +0100, Sebastian Andrzej Siewior wrote:
> * Peter Zijlstra | 2015-01-21 16:07:16 [+0100]:
>
> >On Tue, Jan 20, 2015 at 01:16:13PM -0500, Steven Rostedt wrote:
> >> I'm actually wondering if we should just nuke the _interruptible()
> >> version of swait. As it sho
* Peter Zijlstra | 2015-02-18 15:03:20 [+0100]:
>On Tue, Feb 17, 2015 at 06:44:19PM +0100, Sebastian Andrzej Siewior wrote:
>> * Peter Zijlstra | 2015-01-21 16:07:16 [+0100]:
>>
>> >On Tue, Jan 20, 2015 at 01:16:13PM -0500, Steven Rostedt wrote:
>> >> I'm actually wondering if we should just nuke
On Tue, Feb 17, 2015 at 06:44:19PM +0100, Sebastian Andrzej Siewior wrote:
> * Peter Zijlstra | 2015-01-21 16:07:16 [+0100]:
>
> >On Tue, Jan 20, 2015 at 01:16:13PM -0500, Steven Rostedt wrote:
> >> I'm actually wondering if we should just nuke the _interruptible()
> >> version of swait. As it sho
On Thu, Feb 26, 2015 at 09:23:57PM -0300, Marcelo Tosatti wrote:
> On Tue, Feb 17, 2015 at 06:44:19PM +0100, Sebastian Andrzej Siewior wrote:
> > * Peter Zijlstra | 2015-01-21 16:07:16 [+0100]:
> >
> > >On Tue, Jan 20, 2015 at 01:16:13PM -0500, Steven Rostedt wrote:
> > >> I'm actually wondering i
On 03/05/2015 02:09 AM, Marcelo Tosatti wrote:
>> Can you please include the series?
>>
>> Thanks
>
> Sebastian?
I will pick it up, don't worry. I think I do my -RT day tomorrow.
Sebastian
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* Marcelo Tosatti | 2015-01-14 15:12:52 [-0200]:
Against which tree was this prepared? Could please rebase it against
v3.18.7-rt2? Because a I see "fuzz 2", the mips file is gone and
s390 rejects almost every chunk.
And there was that mips chunk Steven noticed.
Patch #2 seems to apply but since it
On 11/25/2014 12:21 PM, Marcelo Tosatti wrote:
> The problem:
>
> On -RT, an emulated LAPIC timer instances has the following path:
>
> 1) hard interrupt
> 2) ksoftirqd is scheduled
> 3) ksoftirqd wakes up vcpu thread
> 4) vcpu thread is scheduled
>
> This extra context switch introduces unneces
On 11/25/2014 01:57 PM, Rik van Riel wrote:
> On 11/25/2014 12:21 PM, Marcelo Tosatti wrote:
>> The problem:
>>
>> On -RT, an emulated LAPIC timer instances has the following path:
>>
>> 1) hard interrupt
>> 2) ksoftirqd is scheduled
>> 3) ksoftirqd wakes up vcpu thread
>> 4) vcpu thread is schedul
On Tue, Nov 25, 2014 at 01:57:37PM -0500, Rik van Riel wrote:
> On 11/25/2014 12:21 PM, Marcelo Tosatti wrote:
> > The problem:
> >
> > On -RT, an emulated LAPIC timer instances has the following path:
> >
> > 1) hard interrupt
> > 2) ksoftirqd is scheduled
> > 3) ksoftirqd wakes up vcpu thread
>
On Tue, 25 Nov 2014, Rik van Riel wrote:
> On 11/25/2014 12:21 PM, Marcelo Tosatti wrote:
> > The problem:
> >
> > On -RT, an emulated LAPIC timer instances has the following path:
> >
> > 1) hard interrupt
> > 2) ksoftirqd is scheduled
> > 3) ksoftirqd wakes up vcpu thread
> > 4) vcpu thread is
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