* [PATCH] xen: recalculate per-cpupool credits when updating timeslice
@ 2016-01-29 10:21 Juergen Gross
2016-01-29 10:46 ` Jan Beulich
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: Juergen Gross @ 2016-01-29 10:21 UTC (permalink / raw)
To: xen-devel, jbeulich, george.dunlap, dario.faggioli; +Cc: Juergen Gross
When modifying the timeslice of the credit scheduler in a cpupool the
cpupool global credit value (n_cpus * credits_per_tslice) isn't
recalculated. This will lead to wrong scheduling decisions later.
Do the recalculation when updating the timeslice.
Signed-off-by: Juergen Gross <jgross@suse.com>
---
xen/common/sched_credit.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index 03fb2c2..912511e 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -1086,12 +1086,19 @@ csched_dom_cntl(
static inline void
__csched_set_tslice(struct csched_private *prv, unsigned timeslice)
{
+ unsigned long flags;
+
+ spin_lock_irqsave(&prv->lock, flags);
+
prv->tslice_ms = timeslice;
prv->ticks_per_tslice = CSCHED_TICKS_PER_TSLICE;
if ( prv->tslice_ms < prv->ticks_per_tslice )
prv->ticks_per_tslice = 1;
prv->tick_period_us = prv->tslice_ms * 1000 / prv->ticks_per_tslice;
prv->credits_per_tslice = CSCHED_CREDITS_PER_MSEC * prv->tslice_ms;
+ prv->credit = prv->credits_per_tslice * prv->ncpus;
+
+ spin_unlock_irqrestore(&prv->lock, flags);
}
static int
--
2.6.2
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] xen: recalculate per-cpupool credits when updating timeslice
2016-01-29 10:21 [PATCH] xen: recalculate per-cpupool credits when updating timeslice Juergen Gross
@ 2016-01-29 10:46 ` Jan Beulich
[not found] ` <56AB511402000078000CC59C@suse.com>
2016-02-02 7:55 ` Alan Robinson
2 siblings, 0 replies; 7+ messages in thread
From: Jan Beulich @ 2016-01-29 10:46 UTC (permalink / raw)
To: Juergen Gross; +Cc: george.dunlap, dario.faggioli, xen-devel
>>> On 29.01.16 at 11:21, <JGross@suse.com> wrote:
> --- a/xen/common/sched_credit.c
> +++ b/xen/common/sched_credit.c
> @@ -1086,12 +1086,19 @@ csched_dom_cntl(
> static inline void
> __csched_set_tslice(struct csched_private *prv, unsigned timeslice)
> {
> + unsigned long flags;
> +
> + spin_lock_irqsave(&prv->lock, flags);
> +
> prv->tslice_ms = timeslice;
> prv->ticks_per_tslice = CSCHED_TICKS_PER_TSLICE;
> if ( prv->tslice_ms < prv->ticks_per_tslice )
> prv->ticks_per_tslice = 1;
> prv->tick_period_us = prv->tslice_ms * 1000 / prv->ticks_per_tslice;
> prv->credits_per_tslice = CSCHED_CREDITS_PER_MSEC * prv->tslice_ms;
> + prv->credit = prv->credits_per_tslice * prv->ncpus;
> +
> + spin_unlock_irqrestore(&prv->lock, flags);
> }
The added locking, which has no reason give for in the description
at all, puzzles me: I can see it being needed (and having been
missing) when called from csched_sys_cntl(), but it's not clear to
me why it would be needed when called from csched_init(). Yet
csched_sys_cntl() subsequently als updates prv->ratelimit_us,
and hence the lock would perhaps better be taken there?
Jan
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] xen: recalculate per-cpupool credits when updating timeslice
[not found] ` <56AB511402000078000CC59C@suse.com>
@ 2016-01-29 10:59 ` Juergen Gross
2016-02-02 9:53 ` Dario Faggioli
0 siblings, 1 reply; 7+ messages in thread
From: Juergen Gross @ 2016-01-29 10:59 UTC (permalink / raw)
To: Jan Beulich; +Cc: george.dunlap, dario.faggioli, xen-devel
On 29/01/16 11:46, Jan Beulich wrote:
>>>> On 29.01.16 at 11:21, <JGross@suse.com> wrote:
>> --- a/xen/common/sched_credit.c
>> +++ b/xen/common/sched_credit.c
>> @@ -1086,12 +1086,19 @@ csched_dom_cntl(
>> static inline void
>> __csched_set_tslice(struct csched_private *prv, unsigned timeslice)
>> {
>> + unsigned long flags;
>> +
>> + spin_lock_irqsave(&prv->lock, flags);
>> +
>> prv->tslice_ms = timeslice;
>> prv->ticks_per_tslice = CSCHED_TICKS_PER_TSLICE;
>> if ( prv->tslice_ms < prv->ticks_per_tslice )
>> prv->ticks_per_tslice = 1;
>> prv->tick_period_us = prv->tslice_ms * 1000 / prv->ticks_per_tslice;
>> prv->credits_per_tslice = CSCHED_CREDITS_PER_MSEC * prv->tslice_ms;
>> + prv->credit = prv->credits_per_tslice * prv->ncpus;
>> +
>> + spin_unlock_irqrestore(&prv->lock, flags);
>> }
>
> The added locking, which has no reason give for in the description
> at all, puzzles me: I can see it being needed (and having been
> missing) when called from csched_sys_cntl(), but it's not clear to
> me why it would be needed when called from csched_init(). Yet
> csched_sys_cntl() subsequently als updates prv->ratelimit_us,
> and hence the lock would perhaps better be taken there?
The locking is needed to protect against csched_alloc_pdata() and
csched_free_pdata(). prv->credit could be permananently wrong
without the lock, while prv->ratelimit_us can't be modified
concurrently in a wrong way (it could be modified by two concurrent
calls of csched_sys_cntl(), but even with locking one of both
calls would be the winner, same applies to the case with no lock).
OTOH I don't mind moving the lock to csched_sys_cntl(). Dario,
George, any preferences?
Juergen
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] xen: recalculate per-cpupool credits when updating timeslice
2016-01-29 10:21 [PATCH] xen: recalculate per-cpupool credits when updating timeslice Juergen Gross
2016-01-29 10:46 ` Jan Beulich
[not found] ` <56AB511402000078000CC59C@suse.com>
@ 2016-02-02 7:55 ` Alan Robinson
2 siblings, 0 replies; 7+ messages in thread
From: Alan Robinson @ 2016-02-02 7:55 UTC (permalink / raw)
To: Juergen Gross; +Cc: george.dunlap, dario.faggioli, jbeulich, xen-devel
On Fri, Jan 29, 2016 at 11:21:48AM +0100, Juergen Gross wrote:
> When modifying the timeslice of the credit scheduler in a cpupool the
> cpupool global credit value (n_cpus * credits_per_tslice) isn't
> recalculated. This will lead to wrong scheduling decisions later.
>
> Do the recalculation when updating the timeslice.
>
> Signed-off-by: Juergen Gross <jgross@suse.com>
We had notice that the quota's were not working after the timeslice
was changed in a mono-cpupool running two guests doing 'for loops'.
Applied Juergen's patch to a SuSE xen-4.4.3_02-26.2 rpm, the patch
was offset by 6 lines. The guests now observe the quotas when the
timeslice is changed.
Tested-by: Alan.Robinson <alan.robinson@ts.fujitsu.com>
--
Sent from my Fujitsu Primergy RXI300 IA64
Firmenangaben: Fujitsu Technology Solutions GmbH / ts.fujitsu.com/imprint
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] xen: recalculate per-cpupool credits when updating timeslice
2016-01-29 10:59 ` Juergen Gross
@ 2016-02-02 9:53 ` Dario Faggioli
2016-02-02 10:35 ` Juergen Gross
0 siblings, 1 reply; 7+ messages in thread
From: Dario Faggioli @ 2016-02-02 9:53 UTC (permalink / raw)
To: Juergen Gross, Jan Beulich; +Cc: george.dunlap, xen-devel
[-- Attachment #1.1: Type: text/plain, Size: 2620 bytes --]
On Fri, 2016-01-29 at 11:59 +0100, Juergen Gross wrote:
> On 29/01/16 11:46, Jan Beulich wrote:
> > > > > On 29.01.16 at 11:21, <JGross@suse.com> wrote:
> > > --- a/xen/common/sched_credit.c
> > > +++ b/xen/common/sched_credit.c
> > > @@ -1086,12 +1086,19 @@ csched_dom_cntl(
> > > static inline void
> > > __csched_set_tslice(struct csched_private *prv, unsigned
> > > timeslice)
> > > {
> > > + unsigned long flags;
> > > +
> > > + spin_lock_irqsave(&prv->lock, flags);
> > > +
> > > prv->tslice_ms = timeslice;
> > > prv->ticks_per_tslice = CSCHED_TICKS_PER_TSLICE;
> > > if ( prv->tslice_ms < prv->ticks_per_tslice )
> > > prv->ticks_per_tslice = 1;
> > > prv->tick_period_us = prv->tslice_ms * 1000 / prv-
> > > >ticks_per_tslice;
> > > prv->credits_per_tslice = CSCHED_CREDITS_PER_MSEC * prv-
> > > >tslice_ms;
> > > + prv->credit = prv->credits_per_tslice * prv->ncpus;
> > > +
> > > + spin_unlock_irqrestore(&prv->lock, flags);
> > > }
> >
> > The added locking, which has no reason give for in the description
> > at all, puzzles me: I can see it being needed (and having been
> > missing) when called from csched_sys_cntl(), but it's not clear to
> > me why it would be needed when called from csched_init(). Yet
> > csched_sys_cntl() subsequently als updates prv->ratelimit_us,
> > and hence the lock would perhaps better be taken there?
>
> The locking is needed to protect against csched_alloc_pdata() and
> csched_free_pdata(). prv->credit could be permananently wrong
> without the lock, while prv->ratelimit_us can't be modified
> concurrently in a wrong way (it could be modified by two concurrent
> calls of csched_sys_cntl(), but even with locking one of both
> calls would be the winner, same applies to the case with no lock).
>
> OTOH I don't mind moving the lock to csched_sys_cntl(). Dario,
> George, any preferences?
>
Yes, I think having the lock in csched_sys_cntl() would be preferable.
In any case, since the lack of locking and lack of recalculation look
like two pretty independent existing bugs to me, can we have either:
a. two patches;
b. one patch but with both the issues described in the changelog.
My preference going to a.
Thanks and Regards,
Dario
--
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] xen: recalculate per-cpupool credits when updating timeslice
2016-02-02 9:53 ` Dario Faggioli
@ 2016-02-02 10:35 ` Juergen Gross
2016-02-02 11:33 ` Dario Faggioli
0 siblings, 1 reply; 7+ messages in thread
From: Juergen Gross @ 2016-02-02 10:35 UTC (permalink / raw)
To: Dario Faggioli, Jan Beulich; +Cc: george.dunlap, xen-devel
On 02/02/16 10:53, Dario Faggioli wrote:
> On Fri, 2016-01-29 at 11:59 +0100, Juergen Gross wrote:
>> On 29/01/16 11:46, Jan Beulich wrote:
>>>>>> On 29.01.16 at 11:21, <JGross@suse.com> wrote:
>>>> --- a/xen/common/sched_credit.c
>>>> +++ b/xen/common/sched_credit.c
>>>> @@ -1086,12 +1086,19 @@ csched_dom_cntl(
>>>> static inline void
>>>> __csched_set_tslice(struct csched_private *prv, unsigned
>>>> timeslice)
>>>> {
>>>> + unsigned long flags;
>>>> +
>>>> + spin_lock_irqsave(&prv->lock, flags);
>>>> +
>>>> prv->tslice_ms = timeslice;
>>>> prv->ticks_per_tslice = CSCHED_TICKS_PER_TSLICE;
>>>> if ( prv->tslice_ms < prv->ticks_per_tslice )
>>>> prv->ticks_per_tslice = 1;
>>>> prv->tick_period_us = prv->tslice_ms * 1000 / prv-
>>>>> ticks_per_tslice;
>>>> prv->credits_per_tslice = CSCHED_CREDITS_PER_MSEC * prv-
>>>>> tslice_ms;
>>>> + prv->credit = prv->credits_per_tslice * prv->ncpus;
>>>> +
>>>> + spin_unlock_irqrestore(&prv->lock, flags);
>>>> }
>>>
>>> The added locking, which has no reason give for in the description
>>> at all, puzzles me: I can see it being needed (and having been
>>> missing) when called from csched_sys_cntl(), but it's not clear to
>>> me why it would be needed when called from csched_init(). Yet
>>> csched_sys_cntl() subsequently als updates prv->ratelimit_us,
>>> and hence the lock would perhaps better be taken there?
>>
>> The locking is needed to protect against csched_alloc_pdata() and
>> csched_free_pdata(). prv->credit could be permananently wrong
>> without the lock, while prv->ratelimit_us can't be modified
>> concurrently in a wrong way (it could be modified by two concurrent
>> calls of csched_sys_cntl(), but even with locking one of both
>> calls would be the winner, same applies to the case with no lock).
>>
>> OTOH I don't mind moving the lock to csched_sys_cntl(). Dario,
>> George, any preferences?
>>
> Yes, I think having the lock in csched_sys_cntl() would be preferable.
>
> In any case, since the lack of locking and lack of recalculation look
> like two pretty independent existing bugs to me, can we have either:
> a. two patches;
> b. one patch but with both the issues described in the changelog.
>
> My preference going to a.
Without setting prv->credit the lock isn't necessary. In case of a
race domain weights wouldn't be honored correctly for just one
timeslice and I doubt this would be noticeable at all.
OTOH I don't mind splitting the patch into two, I have to respin
anyway.
Juergen
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] xen: recalculate per-cpupool credits when updating timeslice
2016-02-02 10:35 ` Juergen Gross
@ 2016-02-02 11:33 ` Dario Faggioli
0 siblings, 0 replies; 7+ messages in thread
From: Dario Faggioli @ 2016-02-02 11:33 UTC (permalink / raw)
To: Juergen Gross, Jan Beulich; +Cc: george.dunlap, xen-devel
[-- Attachment #1.1: Type: text/plain, Size: 1300 bytes --]
On Tue, 2016-02-02 at 11:35 +0100, Juergen Gross wrote:
> On 02/02/16 10:53, Dario Faggioli wrote:
> >
> > In any case, since the lack of locking and lack of recalculation
> > look
> > like two pretty independent existing bugs to me, can we have
> > either:
> > a. two patches;
> > b. one patch but with both the issues described in the changelog.
> >
> > My preference going to a.
>
> Without setting prv->credit the lock isn't necessary. In case of a
> race domain weights wouldn't be honored correctly for just one
> timeslice and I doubt this would be noticeable at all.
>
Ah, yes, I see what you mean now!!
> OTOH I don't mind splitting the patch into two, I have to respin
> anyway.
>
Well, no, given you explanation above, to which I agree (sory for not
seeing this before), keeping it being just one patch would actually be
better IMO...
But then, please, explain in the changelog that the recalculation would
introduce a race, and hence you also need to lock.
Thanks and regards,
Dario
--
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
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^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2016-02-02 11:33 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-01-29 10:21 [PATCH] xen: recalculate per-cpupool credits when updating timeslice Juergen Gross
2016-01-29 10:46 ` Jan Beulich
[not found] ` <56AB511402000078000CC59C@suse.com>
2016-01-29 10:59 ` Juergen Gross
2016-02-02 9:53 ` Dario Faggioli
2016-02-02 10:35 ` Juergen Gross
2016-02-02 11:33 ` Dario Faggioli
2016-02-02 7:55 ` Alan Robinson
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