Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <7e751be3-c6e9-f89e-ab05-06f9195e3a5f@bytedance.com>
Date:   Thu, 11 May 2023 12:05:23 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0)
 Gecko/20100101 Thunderbird/102.8.0
Subject: Re: [External] Re: [PATCH v2 2/2] sched/core: Avoid double calling
 update_rq_clock()
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mingo@redhat.com, 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: <20230510083450.62334-1-jiahao.os@bytedance.com>
 <20230510083450.62334-3-jiahao.os@bytedance.com>
 <20230510143244.GM4253@hirez.programming.kicks-ass.net>
From:   Hao Jia <jiahao.os@bytedance.com>
In-Reply-To: <20230510143244.GM4253@hirez.programming.kicks-ass.net>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 2023/5/10 Peter Zijlstra wrote:
> On Wed, May 10, 2023 at 04:34:50PM +0800, Hao Jia wrote:

>> For the __balance_push_cpu_stop() case, we remove update_rq_clock() from
>> the __migrate_task() function to avoid double updating the rq clock.
>> And in order to avoid missing rq clock update, add update_rq_clock()
>> call before migration_cpu_stop() calls __migrate_task().
>>
>> For the unthrottle_cfs_rq() case, we use rq_clock_start_loop_update() to
>> prevent multiple calls to update_rq_clock() in unthrottle_cfs_rq().
>>
>> Note that the rq clock has been updated before the set_rq_offline()
>> function runs, so we don't need to call update_rq_clock() in
>> unthrottle_offline_cfs_rqs().
> 
> This reads like 3 separate issues -- in which case this ought to be 3
> separate patches.

I will do it in the next version.

Thanks,
Hao

> 
> 
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index ec7b3e0a2b20..9c712f29e5a4 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -1536,6 +1536,27 @@ static inline void rq_clock_skip_update(struct rq *rq)
>>   	rq->clock_update_flags |= RQCF_REQ_SKIP;
>>   }
>>   
>> +/*
>> + * During cpu offlining and rq wide unthrottling, we can trigger
>> + * an update_rq_clock() for several cfs and rt runqueues (Typically
>> + * when using list_for_each_entry_*)
>> + * rq_clock_start_loop_update() can be called after updating the clock
>> + * once and before iterating over the list to prevent multiple update.
>> + * After the iterative traversal, we need to call rq_clock_stop_loop_update()
>> + * to restore rq->clock_update_flags.
>           ^^^^^^^
>> + */
>> +static inline void rq_clock_start_loop_update(struct rq *rq)
>> +{
>> +	lockdep_assert_rq_held(rq);
>> +	rq->clock_update_flags |= RQCF_ACT_SKIP;
>> +}
>> +
>> +static inline void rq_clock_stop_loop_update(struct rq *rq)
>> +{
>> +	lockdep_assert_rq_held(rq);
>> +	rq->clock_update_flags &= ~RQCF_ACT_SKIP;
>> +}
> 
> This does not restore the flag, it clears the flag.

Thanks for your review.
I will also modify it in the next version.

Thanks,
Hao