linux-kernel - Re: [PATCH v5 4/5] sched/fair: Skip SIS domain scan if fully busy

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Message-ID: <ad2af462-8984-f83a-c9df-d8bf66fbee89@bytedance.com>
Date:   Thu, 15 Sep 2022 11:11:05 +0800
From:   Abel Wu <wuyun.abel@...edance.com>
To:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Josh Don <joshdon@...gle.com>, Chen Yu <yu.c.chen@...el.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/5] sched/fair: Skip SIS domain scan if fully busy

On 9/15/22 8:22 AM, Tim Chen wrote:
> On Fri, 2022-09-09 at 13:53 +0800, Abel Wu wrote:
>> If a full domain scan failed, then no unoccupied cpus available
>> and the LLC is fully busy.  In this case we'd better use cpus
>> more wisely, rather than wasting it trying to find an idle cpu
>> that probably not exist. The fully busy status will be cleared
>> when any cpu of that LLC goes idle and everything goes back to
>> normal again.
>>
>> Make the has_idle_cores boolean hint more rich by turning it
>> into a state machine.
>>
>> Signed-off-by: Abel Wu <wuyun.abel@...edance.com>
>> ---
>>   include/linux/sched/topology.h | 35 +++++++++++++++++-
>>   kernel/sched/fair.c            | 67 ++++++++++++++++++++++++++++------
>>   2 files changed, 89 insertions(+), 13 deletions(-)
>>
>> diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
>> index 816df6cc444e..cc6089765b64 100644
>> --- a/include/linux/sched/topology.h
>> +++ b/include/linux/sched/topology.h
>> @@ -77,10 +77,43 @@ extern int sched_domain_level_max;
>>   
>>   struct sched_group;
>>   
>> +/*
>> + * States of the sched-domain
>> + *
>> + * - sd_has_icores
>> + *	This state is only used in LLC domains to indicate worthy
>> + *	of a full scan in SIS due to idle cores available.
>> + *
>> + * - sd_has_icpus
>> + *	This state indicates that unoccupied (sched-idle/idle) cpus
>> + *	might exist in this domain. For the LLC domains it is the
>> + *	default state since these cpus are the main targets of SIS
>> + *	search, and is also used as a fallback state of the other
>> + *	states.
>> + *
>> + * - sd_is_busy
>> + *	This state indicates there are no unoccupied cpus in this
> 
> Suggest reword to
> 
> .. indicates that all cpus are occupied in this ...

OK, I will make a update in next version!

Thanks,
Abel