Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Greg Kroah-Hartman]

On Thu, Oct 04, 2012 at 12:11:01PM +0800, Huacai Chen wrote:
> Hi, Greg
> 
> I found that Linux-3.5.5 accept this commit "sched: Add missing call
> to calc_load_exit_idle()" but I think this isn't needed. Because
> "5167e8d5417b sched/nohz: Rewrite and fix load-avg computation --
> again not fully applied" is true for 3.6 branch, but not for 3.5
> branch.

But 5167e8d5417b is in 3.5, so shouldn't this commit still be necessary?

> In 3.5 branch, calc_load_exit_idle() is already called in
> tick_nohz_idle_exit(), it doesn't need to be called at
> tick_nohz_update_jiffies() again. In 3.6 branch, some code of
> tick_nohz_idle_exit() is splitted to tick_nohz_restart_sched_tick()
> and calc_load_exit_idle() is missing by accident, so commit "sched:
> Add missing call to calc_load_exit_idle()" is needed.

So this really should be dropped from 3.5?  Charles, Peter, Ingo, any
thoughts here?

thanks,

greg k-h

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Peter Zijlstra]

On Thu, 2012-10-04 at 10:46 -0700, Greg Kroah-Hartman wrote:
> On Thu, Oct 04, 2012 at 12:11:01PM +0800, Huacai Chen wrote:
> > Hi, Greg
> > 
> > I found that Linux-3.5.5 accept this commit "sched: Add missing call
> > to calc_load_exit_idle()" but I think this isn't needed. Because
> > "5167e8d5417b sched/nohz: Rewrite and fix load-avg computation --
> > again not fully applied" is true for 3.6 branch, but not for 3.5
> > branch.
> 
> But 5167e8d5417b is in 3.5, so shouldn't this commit still be necessary?
> 
> > In 3.5 branch, calc_load_exit_idle() is already called in
> > tick_nohz_idle_exit(), it doesn't need to be called at
> > tick_nohz_update_jiffies() again. In 3.6 branch, some code of
> > tick_nohz_idle_exit() is splitted to tick_nohz_restart_sched_tick()
> > and calc_load_exit_idle() is missing by accident, so commit "sched:
> > Add missing call to calc_load_exit_idle()" is needed.
> 
> So this really should be dropped from 3.5?  Charles, Peter, Ingo, any
> thoughts here?

Bah, lots of code movement there recently.. let me try and untangle all
that afresh.. /me checks out v3.5.5.

OK, assuming ->tick_stopped means what the label says, then we only want
to call calc_load_enter_idle() when it flips to 1 and
calc_load_exit_idle() when it flips back to 0, such that when an actual
tick happens its got correct state.

Now the actual patch "5167e8d5417b sched/nohz: Rewrite and fix load-avg
computation -- again not fully applied" modifies
tick_nohz_restart_sched_tick() which doesn't appear to exist in v3.5.5
and the patch fobbed it into tick_nohz_update_jiffies() which is called
from interrupt entry when nohz-idle so that the interrupt (and possible
tailing softirq) see a valid jiffies count.

However, since we don't restart the tick, we won't be sampling load muck
and calling calc_load_exit_idle() from there is bound to confuse state.

I hope.. damn this code ;-)

I can't find wtf went wrong either, the initial patch 5167e8d5417bf5c
contains both hunks, but in that case the fixup 749c8814f0 doesn't make
sense, not can I find anything in merge commits using:

  git log -S calc_load_exit_idle kernel/time/tick-sched.c

/me puzzled

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Greg Kroah-Hartman]

On Thu, Oct 04, 2012 at 08:31:59PM +0200, Peter Zijlstra wrote:
> On Thu, 2012-10-04 at 10:46 -0700, Greg Kroah-Hartman wrote:
> > On Thu, Oct 04, 2012 at 12:11:01PM +0800, Huacai Chen wrote:
> > > Hi, Greg
> > > 
> > > I found that Linux-3.5.5 accept this commit "sched: Add missing call
> > > to calc_load_exit_idle()" but I think this isn't needed. Because
> > > "5167e8d5417b sched/nohz: Rewrite and fix load-avg computation --
> > > again not fully applied" is true for 3.6 branch, but not for 3.5
> > > branch.
> > 
> > But 5167e8d5417b is in 3.5, so shouldn't this commit still be necessary?
> > 
> > > In 3.5 branch, calc_load_exit_idle() is already called in
> > > tick_nohz_idle_exit(), it doesn't need to be called at
> > > tick_nohz_update_jiffies() again. In 3.6 branch, some code of
> > > tick_nohz_idle_exit() is splitted to tick_nohz_restart_sched_tick()
> > > and calc_load_exit_idle() is missing by accident, so commit "sched:
> > > Add missing call to calc_load_exit_idle()" is needed.
> > 
> > So this really should be dropped from 3.5?  Charles, Peter, Ingo, any
> > thoughts here?
> 
> Bah, lots of code movement there recently.. let me try and untangle all
> that afresh.. /me checks out v3.5.5.
> 
> OK, assuming ->tick_stopped means what the label says, then we only want
> to call calc_load_enter_idle() when it flips to 1 and
> calc_load_exit_idle() when it flips back to 0, such that when an actual
> tick happens its got correct state.
> 
> Now the actual patch "5167e8d5417b sched/nohz: Rewrite and fix load-avg
> computation -- again not fully applied" modifies
> tick_nohz_restart_sched_tick() which doesn't appear to exist in v3.5.5
> and the patch fobbed it into tick_nohz_update_jiffies() which is called
> from interrupt entry when nohz-idle so that the interrupt (and possible
> tailing softirq) see a valid jiffies count.
> 
> However, since we don't restart the tick, we won't be sampling load muck
> and calling calc_load_exit_idle() from there is bound to confuse state.
> 
> I hope.. damn this code ;-)
> 
> I can't find wtf went wrong either, the initial patch 5167e8d5417bf5c
> contains both hunks, but in that case the fixup 749c8814f0 doesn't make
> sense, not can I find anything in merge commits using:
> 
>   git log -S calc_load_exit_idle kernel/time/tick-sched.c
> 
> /me puzzled

I'm puzzled as well.  Any ideas if I should do anything here or not?

greg k-h

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Peter Zijlstra]

On Thu, 2012-10-04 at 15:27 -0700, Greg Kroah-Hartman wrote:
> I'm puzzled as well.  Any ideas if I should do anything here or not?

So I think the current v3.5.5 code is fine. I'm just not smart enough to
figure out how 3.6 got fuzzed, this git thing is confusing as hell.

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Greg Kroah-Hartman]

On Fri, Oct 05, 2012 at 12:21:06PM +0200, Peter Zijlstra wrote:
> On Thu, 2012-10-04 at 15:27 -0700, Greg Kroah-Hartman wrote:
> > I'm puzzled as well.  Any ideas if I should do anything here or not?
> 
> So I think the current v3.5.5 code is fine. I'm just not smart enough to
> figure out how 3.6 got fuzzed, this git thing is confusing as hell.

Thanks for letting me know, and digging through this, I'll leave things
as-is.

greg k-h

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Jonathan Nieder]

Peter Zijlstra wrote:
> On Thu, 2012-10-04 at 15:27 -0700, Greg Kroah-Hartman wrote:

>> I'm puzzled as well.  Any ideas if I should do anything here or not?
>
> So I think the current v3.5.5 code is fine.

Now I'm puzzled.  You wrote:

| However, since we don't restart the tick, we won't be sampling load muck
| and calling calc_load_exit_idle() from there is bound to confuse state.

Doesn't that mean 900404e5d201 "sched: Add missing call to
calc_load_exit_idle()" which is part of 3.5.5 was problematic?  Or
did I just miscount the number of "not"s?

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Peter Zijlstra]

On Fri, 2012-10-05 at 10:10 -0700, Jonathan Nieder wrote:
> Peter Zijlstra wrote:
> > On Thu, 2012-10-04 at 15:27 -0700, Greg Kroah-Hartman wrote:
> 
> >> I'm puzzled as well.  Any ideas if I should do anything here or not?
> >
> > So I think the current v3.5.5 code is fine.
> 
> Now I'm puzzled.  You wrote:
> 
> | However, since we don't restart the tick, we won't be sampling load muck
> | and calling calc_load_exit_idle() from there is bound to confuse state.
> 
> Doesn't that mean 900404e5d201 "sched: Add missing call to
> calc_load_exit_idle()" which is part of 3.5.5 was problematic?  Or
> did I just miscount the number of "not"s?


Argh, yeah, so now I've managed to confuse everyone I'm afraid.

You are right, v3.5.5 has one calc_load_exit_idle() too many, the one in
tick_nohz_update_jiffies() needs to go.

Sorry.. I got entirely confused figuring out wth happened with 3.6.

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Charles Wang]

On 10/06/2012 01:23 AM, Peter Zijlstra wrote:
> On Fri, 2012-10-05 at 10:10 -0700, Jonathan Nieder wrote:
>> Peter Zijlstra wrote:
>>> On Thu, 2012-10-04 at 15:27 -0700, Greg Kroah-Hartman wrote:
>>
>>>> I'm puzzled as well.  Any ideas if I should do anything here or not?
>>>
>>> So I think the current v3.5.5 code is fine.
>>
>> Now I'm puzzled.  You wrote:
>>
>> | However, since we don't restart the tick, we won't be sampling load muck
>> | and calling calc_load_exit_idle() from there is bound to confuse state.
>>
>> Doesn't that mean 900404e5d201 "sched: Add missing call to
>> calc_load_exit_idle()" which is part of 3.5.5 was problematic?  Or
>> did I just miscount the number of "not"s?
>
>
> Argh, yeah, so now I've managed to confuse everyone I'm afraid.
>
> You are right, v3.5.5 has one calc_load_exit_idle() too many, the one in
> tick_nohz_update_jiffies() needs to go.
>
> Sorry.. I got entirely confused figuring out wth happened with 3.6.
>
High loadavg reported with v3.6, and I just checked the upstream code, 
which puzzled many people. Sorry for that~

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Jonathan Nieder]

Peter Zijlstra wrote:

> I can't find wtf went wrong either, the initial patch 5167e8d5417bf5c
> contains both hunks, but in that case the fixup 749c8814f0 doesn't make
> sense, not can I find anything in merge commits using:
>
>   git log -S calc_load_exit_idle kernel/time/tick-sched.c

 git log -m -p --first-parent -Scalc_load_exit_idle -- kernel/time/tick-sched.c

finds 3992c0321258 ("Merge branch 'timers-core-for-linus'",
2012-07-22), which seems to have mismerged 2ac0d98fd624 ("nohz: Make
nohz API agnostic against idle ticks cputime accounting").

Thanks,
Jonathan

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Charles Wang]

On 10/05/2012 09:39 AM, Jonathan Nieder wrote:
> Peter Zijlstra wrote:
>
>> I can't find wtf went wrong either, the initial patch 5167e8d5417bf5c
>> contains both hunks, but in that case the fixup 749c8814f0 doesn't make
>> sense, not can I find anything in merge commits using:
>>
>>    git log -S calc_load_exit_idle kernel/time/tick-sched.c
>
>   git log -m -p --first-parent -Scalc_load_exit_idle -- kernel/time/tick-sched.c
>
> finds 3992c0321258 ("Merge branch 'timers-core-for-linus'",
> 2012-07-22), which seems to have mismerged 2ac0d98fd624 ("nohz: Make
> nohz API agnostic against idle ticks cputime accounting").
That's it.  Patch 2ac0d98fd624 and 19f5f7364("nohz: Separate idle 
sleeping time accounting from nohz logic") are produced on 2011-07-28, 
merged on 2012-07-22, right after 5167e8d5417bf5c, but applied before 
5167e8d5417bf5c.
These two patches changed tick_nohz_idle_exit, which causing Peter's 
patch 5167e8d5417bf5c couldn't fully be applied.
There should be conflict being reported, but why we don't get is really 
confused.
>
> Thanks,
> Jonathan
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Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[陈华才]

My opinion: The original patch "sched/nohz: Rewrite and fix load-avg
computation -- again" is designed for 3.5-branch and calc_load_exit_idle()
is called directly in tick_nohz_idle_exit(). So, the patch can be fully
applied in 3.5 and doesn't need to fix (Add the missing call), but not
fully applied in 3.6 (because code splitted) and need to fix.



> On Thu, Oct 04, 2012 at 08:31:59PM +0200, Peter Zijlstra wrote:
>> On Thu, 2012-10-04 at 10:46 -0700, Greg Kroah-Hartman wrote:
>> > On Thu, Oct 04, 2012 at 12:11:01PM +0800, Huacai Chen wrote:
>> > > Hi, Greg
>> > >
>> > > I found that Linux-3.5.5 accept this commit "sched: Add missing call
>> > > to calc_load_exit_idle()" but I think this isn't needed. Because
>> > > "5167e8d5417b sched/nohz: Rewrite and fix load-avg computation --
>> > > again not fully applied" is true for 3.6 branch, but not for 3.5
>> > > branch.
>> >
>> > But 5167e8d5417b is in 3.5, so shouldn't this commit still be
>> necessary?
>> >
>> > > In 3.5 branch, calc_load_exit_idle() is already called in
>> > > tick_nohz_idle_exit(), it doesn't need to be called at
>> > > tick_nohz_update_jiffies() again. In 3.6 branch, some code of
>> > > tick_nohz_idle_exit() is splitted to tick_nohz_restart_sched_tick()
>> > > and calc_load_exit_idle() is missing by accident, so commit "sched:
>> > > Add missing call to calc_load_exit_idle()" is needed.
>> >
>> > So this really should be dropped from 3.5?  Charles, Peter, Ingo, any
>> > thoughts here?
>>
>> Bah, lots of code movement there recently.. let me try and untangle all
>> that afresh.. /me checks out v3.5.5.
>>
>> OK, assuming ->tick_stopped means what the label says, then we only want
>> to call calc_load_enter_idle() when it flips to 1 and
>> calc_load_exit_idle() when it flips back to 0, such that when an actual
>> tick happens its got correct state.
>>
>> Now the actual patch "5167e8d5417b sched/nohz: Rewrite and fix load-avg
>> computation -- again not fully applied" modifies
>> tick_nohz_restart_sched_tick() which doesn't appear to exist in v3.5.5
>> and the patch fobbed it into tick_nohz_update_jiffies() which is called
>> from interrupt entry when nohz-idle so that the interrupt (and possible
>> tailing softirq) see a valid jiffies count.
>>
>> However, since we don't restart the tick, we won't be sampling load muck
>> and calling calc_load_exit_idle() from there is bound to confuse state.
>>
>> I hope.. damn this code ;-)
>>
>> I can't find wtf went wrong either, the initial patch 5167e8d5417bf5c
>> contains both hunks, but in that case the fixup 749c8814f0 doesn't make
>> sense, not can I find anything in merge commits using:
>>
>>   git log -S calc_load_exit_idle kernel/time/tick-sched.c
>>
>> /me puzzled
>
> I'm puzzled as well.  Any ideas if I should do anything here or not?
>
> greg k-h
>


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Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[陈华才]

So I still think that "sched: Add missing call to calc_load_exit_idle()"
should be reverted in 3.5 branch...

> On 10/06/2012 01:23 AM, Peter Zijlstra wrote:
>> On Fri, 2012-10-05 at 10:10 -0700, Jonathan Nieder wrote:
>>> Peter Zijlstra wrote:
>>>> On Thu, 2012-10-04 at 15:27 -0700, Greg Kroah-Hartman wrote:
>>>
>>>>> I'm puzzled as well.  Any ideas if I should do anything here or not?
>>>>
>>>> So I think the current v3.5.5 code is fine.
>>>
>>> Now I'm puzzled.  You wrote:
>>>
>>> | However, since we don't restart the tick, we won't be sampling load
>>> muck
>>> | and calling calc_load_exit_idle() from there is bound to confuse
>>> state.
>>>
>>> Doesn't that mean 900404e5d201 "sched: Add missing call to
>>> calc_load_exit_idle()" which is part of 3.5.5 was problematic?  Or
>>> did I just miscount the number of "not"s?
>>
>>
>> Argh, yeah, so now I've managed to confuse everyone I'm afraid.
>>
>> You are right, v3.5.5 has one calc_load_exit_idle() too many, the one in
>> tick_nohz_update_jiffies() needs to go.
>>
>> Sorry.. I got entirely confused figuring out wth happened with 3.6.
>>
> High loadavg reported with v3.6, and I just checked the upstream code,
> which puzzled many people. Sorry for that~
>

Re: Seems like "sched: Add missing call to calc_load_exit_idle()" should be reverted in 3.5 branch

[Greg Kroah-Hartman]

On Sat, Oct 13, 2012 at 11:39:37AM +0800, 陈华才 wrote:
> So I still think that "sched: Add missing call to calc_load_exit_idle()"
> should be reverted in 3.5 branch...

3.5 is now end-of-life, with no more releases, everyone should have
moved off of it to 3.6 now, so there's nothing to do here anymore.

thanks,

greg k-h