From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: luca abeni <luca.abeni@santannapisa.it>,
Ingo Molnar <mingo@kernel.org>,
Juri Lelli <juri.lelli@redhat.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Valentin Schneider <Valentin.Schneider@arm.com>,
Qais Yousef <Qais.Yousef@arm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/5] sched/deadline: Use return value of SCHED_WARN_ON() in bw accounting
Date: Tue, 30 Jul 2019 17:08:35 +0100 [thread overview]
Message-ID: <7da6555c-baff-39df-b562-2510566ba4bf@arm.com> (raw)
In-Reply-To: <20190730082316.GK31381@hirez.programming.kicks-ass.net>
On 7/30/19 9:23 AM, Peter Zijlstra wrote:
> On Mon, Jul 29, 2019 at 05:59:04PM +0100, Dietmar Eggemann wrote:
>> On 7/29/19 5:54 PM, Peter Zijlstra wrote:
>>> On Fri, Jul 26, 2019 at 12:18:19PM +0200, luca abeni wrote:
>>>> Hi Dietmar,
>>>>
>>>> On Fri, 26 Jul 2019 09:27:56 +0100
>>>> Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>>>>
>>>>> To make the decision whether to set rq or running bw to 0 in underflow
>>>>> case use the return value of SCHED_WARN_ON() rather than an extra if
>>>>> condition.
>>>>
>>>> I think I tried this at some point, but if I remember well this
>>>> solution does not work correctly when SCHED_DEBUG is not enabled.
>>>
>>> Well, it 'works' in so far that it compiles. But it might not be what
>>> one expects. That is, for !SCHED_DEBUG the return value is an
>>> unconditional false.
>>>
>>> In this case I think that's fine, the WARN _should_ not be happending.
>>
>> But there is commit 6d3aed3d ("sched/debug: Fix SCHED_WARN_ON() to
>> return a value on !CONFIG_SCHED_DEBUG as well")?
>>
>> But it doesn't work with !CONFIG_SCHED_DEBUG
>>
>> What compiles and work is (at least on Arm64).
>>
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index 4012f98b9d26..494a767a4091 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -78,7 +78,7 @@
>> #ifdef CONFIG_SCHED_DEBUG
>> # define SCHED_WARN_ON(x) WARN_ONCE(x, #x)
>> #else
>> -# define SCHED_WARN_ON(x) ({ (void)(x), 0; })
>> +# define SCHED_WARN_ON(x) ({ (void)(x), x; })
>
> Why doesn't the ,0 compile? That should work just fine. The thing is,
> the two existing users:
>
> kernel/sched/fair.c: if (SCHED_WARN_ON(!se->on_rq))
> kernel/sched/fair.c: if (SCHED_WARN_ON(!se->on_rq))
>
> seem to compile just fine with it.
You're right, compiling is not an issue. But it looks like the code does
different things depending on CONFIG_SCHED_DEBUG.
E.g. in set_last_buddy() we would return if '!se->on_rq' with
CONFIG_SCHED_DEBUG and continue the for_each_sched_entity() with
!CONFIG_SCHED_DEBUG.
IMHO, this forced Luca e.g. in __sub_running_bw() to code:
SCHED_WARN_ON(dl_rq->running_bw > old);
if (dl_rq->running_bw > old)
dl_rq->running_bw = 0;
and not:
if (SCHED_WARN_ON(dl_rq->running_bw > old))
dl_rq->running_bw = 0;
I experimented with '# define SCHED_WARN_ON(x) ({ (void)(x), x; })' and
in this case code inside an 'if (SCHED_WARN_ON(cond))' is also executed
with !CONFIG_SCHED_DEBUG.
prev parent reply other threads:[~2019-07-30 16:08 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-26 8:27 [PATCH 0/5] sched/deadline: Fix double accounting in push_dl_task() & some cleanups Dietmar Eggemann
2019-07-26 8:27 ` [PATCH 1/5] sched/deadline: Fix double accounting of rq/running bw in push_dl_task() Dietmar Eggemann
2019-07-26 10:11 ` luca abeni
2019-07-29 8:59 ` Dietmar Eggemann
2019-07-29 16:10 ` Peter Zijlstra
2019-07-26 13:30 ` luca abeni
2019-07-29 9:00 ` Dietmar Eggemann
2019-07-31 10:32 ` Dietmar Eggemann
2019-07-26 8:27 ` [PATCH 2/5] sched/deadline: Remove unused int flags from __dequeue_task_dl() Dietmar Eggemann
2019-07-29 16:35 ` Peter Zijlstra
2019-07-29 17:12 ` Dietmar Eggemann
2019-07-26 8:27 ` [PATCH 3/5] sched/deadline: Use __sub_running_bw() throughout dl_change_utilization() Dietmar Eggemann
2019-07-29 16:47 ` Peter Zijlstra
2019-07-29 17:21 ` Dietmar Eggemann
2019-07-26 8:27 ` [PATCH 4/5] sched/deadline: Cleanup on_dl_rq() handling Dietmar Eggemann
2019-07-26 8:37 ` Valentin Schneider
2019-07-26 8:58 ` Qais Yousef
2019-07-26 9:20 ` Juri Lelli
2019-07-26 9:32 ` Valentin Schneider
2019-07-29 16:49 ` Peter Zijlstra
2019-07-30 6:41 ` Juri Lelli
2019-07-30 8:21 ` Peter Zijlstra
2019-07-31 17:32 ` Dietmar Eggemann
2019-07-31 20:20 ` luca abeni
2019-08-01 16:01 ` Dietmar Eggemann
2019-07-26 8:27 ` [PATCH 5/5] sched/deadline: Use return value of SCHED_WARN_ON() in bw accounting Dietmar Eggemann
2019-07-26 10:18 ` luca abeni
2019-07-29 16:54 ` Peter Zijlstra
2019-07-29 16:59 ` Dietmar Eggemann
2019-07-30 8:23 ` Peter Zijlstra
2019-07-30 16:08 ` Dietmar Eggemann [this message]
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