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Message-ID: <612c77f3-2983-b010-a4ef-4fbaf57064b5@bytedance.com>
Date:   Tue, 4 Apr 2023 17:06:39 +0800
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Subject: Re: [External] Re: [PATCH v3] sched/core: Adapt WARN_DOUBLE_CLOCK
 machinery for core-sched
To:     Phil Auld <pauld@redhat.com>
Cc:     mingo@redhat.com, peterz@infradead.org, mingo@kernel.org,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com,
        mgorman@techsingularity.net, linux-kernel@vger.kernel.org
References: <20230330035827.16937-1-jiahao.os@bytedance.com>
 <20230331125813.GA782283@lorien.usersys.redhat.com>
From:   Hao Jia <jiahao.os@bytedance.com>
In-Reply-To: <20230331125813.GA782283@lorien.usersys.redhat.com>
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On 2023/3/31 Phil Auld wrote:
> Hi,
> 
> On Thu, Mar 30, 2023 at 11:58:27AM +0800 Hao Jia wrote:
>> When sched_core_enabled(), we sometimes need to call update_rq_clock()
>> to update the rq clock of sibling CPUs on the same core, before that we
>> need to clear RQCF_UPDATED of rq->clock_update_flags to avoid the
>> WARN_DOUBLE_CLOCK warning. Because at this time the rq->clock_update_flags
>> of sibling CPUs may be RQCF_UPDATED. If sched_core_enabled(), we will get
>> a core wide rq->lock, so at this point we can safely clear RQCF_UPDATED of
>> rq->clock_update_flags of all CPUs on this core to avoid the
>> WARN_DOUBLE_CLOCK warning.
>>
>> We sometimes use rq_pin_lock() and raw_spin_rq_lock() separately,
>> For example newidle_balance() and _double_lock_balance(). We will
>> temporarily give up core wide rq->lock, and then use raw_spin_rq_lock()
>> to reacquire core wide rq->lock without rq_pin_lock(), so We can not
>> clear RQCF_UPDATED of rq->clock_update_flags of other cpus on the
>> same core in rq_pin_lock().
>>
>> Steps to reproduce:
>> 1. Enable CONFIG_SCHED_DEBUG and CONFIG_SCHED_CORE when compiling
>>     the kernel
>> 2. echo 1 > /sys/kernel/debug/clear_warn_once
>>     echo "WARN_DOUBLE_CLOCK" > /sys/kernel/debug/sched/features
>> 3. Run the linux/tools/testing/selftests/sched/cs_prctl_test test
>>
>> Signed-off-by: Hao Jia <jiahao.os@bytedance.com>
> 
> I think this looks good. One small nit is that I think you might
> replace "core wide" with "core-wide" everywhere.
> 
> 
> Reviewed-by: Phil Auld <pauld@redhat.com>
> 

Thank you for your review, I will do it in the next version.

Thanks,
Hao