Re: PATCH [0/4] perf: clean-up of power events API

Re: PATCH [0/4] perf: clean-up of power events API

[Ingo Molnar]

* Thomas Renninger <trenn@suse.de> wrote:

> > Most definitely. It's no accident that it took such a long time for this issue 
> > to be raised in the first place. It's a rare occurance -
>
> Do you agree that this occurance happened now and these events should get cleaned 
> up before ARM and other archs make use of the broken interface?
>
> If not, discussing this further, is a big waste of time... and Jean would have to 
> try to adapt his ARM code on the broken ABI...

The discussion seems to have died down somewhat. Please re-send to lkml the latest 
patches you have to remind everyone of the latest state of things - the merge window 
is getting near.

My only compatibility/ABI point is basically that it shouldnt break _existing_ 
tracepoints (and users thereof). If your latest bits meet that then it ought to be a 
good first step. You are free to (and encouraged to) introduce more complete sets of 
events.

Thanks,

	Ingo

Re: PATCH [0/4] perf: clean-up of power events API

[Peter Zijlstra]

On Tue, 2010-10-19 at 13:45 +0200, Ingo Molnar wrote:
> 
> * Thomas Renninger <trenn@suse.de> wrote:
> 
> > > Most definitely. It's no accident that it took such a long time for this issue 
> > > to be raised in the first place. It's a rare occurance -
> >
> > Do you agree that this occurance happened now and these events should get cleaned 
> > up before ARM and other archs make use of the broken interface?
> >
> > If not, discussing this further, is a big waste of time... and Jean would have to 
> > try to adapt his ARM code on the broken ABI...
> 
> The discussion seems to have died down somewhat. Please re-send to lkml the latest 
> patches you have to remind everyone of the latest state of things - the merge window 
> is getting near.
> 
> My only compatibility/ABI point is basically that it shouldnt break _existing_ 
> tracepoints (and users thereof). If your latest bits meet that then it ought to be a 
> good first step. You are free to (and encouraged to) introduce more complete sets of 
> events.

Can we deprecate and eventually remove the old ones, or will we be
forever obliged to carry the old ones too?

Re: PATCH [0/4] perf: clean-up of power events API

[Ingo Molnar]

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Tue, 2010-10-19 at 13:45 +0200, Ingo Molnar wrote:
> > 
> > * Thomas Renninger <trenn@suse.de> wrote:
> > 
> > > > Most definitely. It's no accident that it took such a long time for this issue 
> > > > to be raised in the first place. It's a rare occurance -
> > >
> > > Do you agree that this occurance happened now and these events should get cleaned 
> > > up before ARM and other archs make use of the broken interface?
> > >
> > > If not, discussing this further, is a big waste of time... and Jean would have to 
> > > try to adapt his ARM code on the broken ABI...
> > 
> > The discussion seems to have died down somewhat. Please re-send to lkml the latest 
> > patches you have to remind everyone of the latest state of things - the merge window 
> > is getting near.
> > 
> > My only compatibility/ABI point is basically that it shouldnt break _existing_ 
> > tracepoints (and users thereof). If your latest bits meet that then it ought to be a 
> > good first step. You are free to (and encouraged to) introduce more complete sets of 
> > events.
> 
> Can we deprecate and eventually remove the old ones, or will we be forever obliged 
> to carry the old ones too?

We most definitely want to deprecate and remove the old ones - but we want to give 
instrumentation software some migration time for that.

Jean, Arjan, what would be a feasible and practical deprecation period for that? One 
kernel cycle?

Thanks,

	Ingo

Re: PATCH [0/4] perf: clean-up of power events API

[Arjan van de Ven]

  On 10/19/2010 4:52 AM, Ingo Molnar wrote:
> * Peter Zijlstra<peterz@infradead.org>  wrote:
>
>> On Tue, 2010-10-19 at 13:45 +0200, Ingo Molnar wrote:
>>> * Thomas Renninger<trenn@suse.de>  wrote:
>>>
>>>>> Most definitely. It's no accident that it took such a long time for this issue
>>>>> to be raised in the first place. It's a rare occurance -
>>>> Do you agree that this occurance happened now and these events should get cleaned
>>>> up before ARM and other archs make use of the broken interface?
>>>>
>>>> If not, discussing this further, is a big waste of time... and Jean would have to
>>>> try to adapt his ARM code on the broken ABI...
>>> The discussion seems to have died down somewhat. Please re-send to lkml the latest
>>> patches you have to remind everyone of the latest state of things - the merge window
>>> is getting near.
>>>
>>> My only compatibility/ABI point is basically that it shouldnt break _existing_
>>> tracepoints (and users thereof). If your latest bits meet that then it ought to be a
>>> good first step. You are free to (and encouraged to) introduce more complete sets of
>>> events.
>> Can we deprecate and eventually remove the old ones, or will we be forever obliged
>> to carry the old ones too?
> We most definitely want to deprecate and remove the old ones - but we want to give
> instrumentation software some migration time for that.
>
> Jean, Arjan, what would be a feasible and practical deprecation period for that? One
> kernel cycle?

more like a year

for some time software needs to support both, especially if popular 
distros stick to an older kernel like *cough* RHEL6

Re: PATCH [0/4] perf: clean-up of power events API

[Ingo Molnar]

* Arjan van de Ven <arjan@linux.intel.com> wrote:

>  On 10/19/2010 4:52 AM, Ingo Molnar wrote:
> >* Peter Zijlstra<peterz@infradead.org>  wrote:
> >
> >>On Tue, 2010-10-19 at 13:45 +0200, Ingo Molnar wrote:
> >>>* Thomas Renninger<trenn@suse.de>  wrote:
> >>>
> >>>>>Most definitely. It's no accident that it took such a long time for this issue
> >>>>>to be raised in the first place. It's a rare occurance -
> >>>>Do you agree that this occurance happened now and these events should get cleaned
> >>>>up before ARM and other archs make use of the broken interface?
> >>>>
> >>>>If not, discussing this further, is a big waste of time... and Jean would have to
> >>>>try to adapt his ARM code on the broken ABI...
> >>>The discussion seems to have died down somewhat. Please re-send to lkml the latest
> >>>patches you have to remind everyone of the latest state of things - the merge window
> >>>is getting near.
> >>>
> >>>My only compatibility/ABI point is basically that it shouldnt break _existing_
> >>>tracepoints (and users thereof). If your latest bits meet that then it ought to be a
> >>>good first step. You are free to (and encouraged to) introduce more complete sets of
> >>>events.
> >>Can we deprecate and eventually remove the old ones, or will we be forever obliged
> >>to carry the old ones too?
> >We most definitely want to deprecate and remove the old ones - but we want to give
> >instrumentation software some migration time for that.
> >
> >Jean, Arjan, what would be a feasible and practical deprecation period for that? One
> >kernel cycle?
> 
> more like a year
> 
> for some time software needs to support both, especially if popular distros stick 
> to an older kernel like *cough* RHEL6

Sure, you can support both. But as long as support for the _new_ events is included 
in PowerTop there's no need to keep the duality upstream. Running ancient PowerTop 
on fresh kernels is not common.

An old RHEL kernel will still keep on working as you can keep support for old events 
in PowerTop as long as you wish to.

The new kernel also wont 'overwrite' old events with new definitions in the future, 
so PowerTop will keep working for as long as you want to support older kernels.

Does that sound good?

Thanks,

	Ingo

Re: PATCH [0/4] perf: clean-up of power events API

[Arjan van de Ven]

  On 10/19/2010 6:50 AM, Ingo Molnar wrote:
> * Arjan van de Ven<arjan@linux.intel.com>  wrote:
>
>>   On 10/19/2010 4:52 AM, Ingo Molnar wrote:
>>> * Peter Zijlstra<peterz@infradead.org>   wrote:
>>>
>>>> On Tue, 2010-10-19 at 13:45 +0200, Ingo Molnar wrote:
>>>>> * Thomas Renninger<trenn@suse.de>   wrote:
>>>>>
>>>>>>> Most definitely. It's no accident that it took such a long time for this issue
>>>>>>> to be raised in the first place. It's a rare occurance -
>>>>>> Do you agree that this occurance happened now and these events should get cleaned
>>>>>> up before ARM and other archs make use of the broken interface?
>>>>>>
>>>>>> If not, discussing this further, is a big waste of time... and Jean would have to
>>>>>> try to adapt his ARM code on the broken ABI...
>>>>> The discussion seems to have died down somewhat. Please re-send to lkml the latest
>>>>> patches you have to remind everyone of the latest state of things - the merge window
>>>>> is getting near.
>>>>>
>>>>> My only compatibility/ABI point is basically that it shouldnt break _existing_
>>>>> tracepoints (and users thereof). If your latest bits meet that then it ought to be a
>>>>> good first step. You are free to (and encouraged to) introduce more complete sets of
>>>>> events.
>>>> Can we deprecate and eventually remove the old ones, or will we be forever obliged
>>>> to carry the old ones too?
>>> We most definitely want to deprecate and remove the old ones - but we want to give
>>> instrumentation software some migration time for that.
>>>
>>> Jean, Arjan, what would be a feasible and practical deprecation period for that? One
>>> kernel cycle?
>> more like a year
>>
>> for some time software needs to support both, especially if popular distros stick
>> to an older kernel like *cough* RHEL6
> Sure, you can support both. But as long as support for the _new_ events is included
> in PowerTop there's no need to keep the duality upstream. Running ancient PowerTop
> on fresh kernels is not common.
>
> An old RHEL kernel will still keep on working as you can keep support for old events
> in PowerTop as long as you wish to.
>
> The new kernel also wont 'overwrite' old events with new definitions in the future,
> so PowerTop will keep working for as long as you want to support older kernels.
>
> Does that sound good?

this does not scale much long term, eg this only works if this is only 
done once, and these points are stable afterwards.
otherwise we get 25 of those different  "workarounds for kernel ABI 
breakage" into all different projects, and it becomes
untestable for all the poor software writers...

Re: PATCH [0/4] perf: clean-up of power events API

[Ingo Molnar]

* Arjan van de Ven <arjan@linux.intel.com> wrote:

> >> for some time software needs to support both, especially if popular distros 
> >> stick to an older kernel like *cough* RHEL6
> >
> > Sure, you can support both. But as long as support for the _new_ events is 
> > included in PowerTop there's no need to keep the duality upstream. Running 
> > ancient PowerTop on fresh kernels is not common.
> >
> > An old RHEL kernel will still keep on working as you can keep support for old 
> > events in PowerTop as long as you wish to.
> >
> > The new kernel also wont 'overwrite' old events with new definitions in the 
> > future, so PowerTop will keep working for as long as you want to support older 
> > kernels.
> >
> > Does that sound good?
> 
> this does not scale much long term, eg this only works if this is only done once, 
> and these points are stable afterwards. otherwise we get 25 of those different 
> "workarounds for kernel ABI breakage" into all different projects, and it becomes 
> untestable for all the poor software writers...

I have no intention for this to become common. For the 2+ years tracepoints have 
been upstream this is the first time it has come up. It's a rare occurance, and as 
long as we keep it rare and as long as we have a smooth transition process in place 
it should be good. If it becomes common we are doing something wrong ...

Alternatively you might want to review the new power events and suggest ways to add 
that extra information to existing events that suits your purposes as well. You 
added the old power tracepoints so you sure must have an opinion about it all?

Thanks,

	Ingo