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From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
	Morten Rasmussen <morten.rasmussen@arm.com>,
	Tim Chen <tim.c.chen@linux.intel.com>
Cc: "valentin.schneider@arm.com" <valentin.schneider@arm.com>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"will@kernel.org" <will@kernel.org>,
	"rjw@rjwysocki.net" <rjw@rjwysocki.net>,
	"vincent.guittot@linaro.org" <vincent.guittot@linaro.org>,
	"lenb@kernel.org" <lenb@kernel.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	Jonathan Cameron <jonathan.cameron@huawei.com>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"juri.lelli@redhat.com" <juri.lelli@redhat.com>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"bsegall@google.com" <bsegall@google.com>,
	"mgorman@suse.de" <mgorman@suse.de>,
	"mark.rutland@arm.com" <mark.rutland@arm.com>,
	"sudeep.holla@arm.com" <sudeep.holla@arm.com>,
	"aubrey.li@linux.intel.com" <aubrey.li@linux.intel.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"linuxarm@openeuler.org" <linuxarm@openeuler.org>,
	"xuwei (O)" <xuwei5@huawei.com>,
	"Zengtao (B)" <prime.zeng@hisilicon.com>,
	"tiantao (H)" <tiantao6@hisilicon.com>
Subject: Re: [RFC PATCH v3 0/2] scheduler: expose the topology of clusters and add cluster scheduler
Date: Tue, 26 Jan 2021 12:02:21 +0100
Message-ID: <bf0edcb6-6dc7-5591-35ac-08e94bf7dce9@arm.com> (raw)
In-Reply-To: <076088f4daf64727b1587b162eb08dda@hisilicon.com>

On 25/01/2021 11:50, Song Bao Hua (Barry Song) wrote:
> 
>> -----Original Message-----
>> From: Dietmar Eggemann [mailto:dietmar.eggemann@arm.com]
>> Sent: Wednesday, January 13, 2021 12:00 AM
>> To: Morten Rasmussen <morten.rasmussen@arm.com>; Tim Chen
>> <tim.c.chen@linux.intel.com>
>> Cc: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>;
>> valentin.schneider@arm.com; catalin.marinas@arm.com; will@kernel.org;
>> rjw@rjwysocki.net; vincent.guittot@linaro.org; lenb@kernel.org;
>> gregkh@linuxfoundation.org; Jonathan Cameron <jonathan.cameron@huawei.com>;
>> mingo@redhat.com; peterz@infradead.org; juri.lelli@redhat.com;
>> rostedt@goodmis.org; bsegall@google.com; mgorman@suse.de;
>> mark.rutland@arm.com; sudeep.holla@arm.com; aubrey.li@linux.intel.com;
>> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
>> linux-acpi@vger.kernel.org; linuxarm@openeuler.org; xuwei (O)
>> <xuwei5@huawei.com>; Zengtao (B) <prime.zeng@hisilicon.com>; tiantao (H)
>> <tiantao6@hisilicon.com>
>> Subject: Re: [RFC PATCH v3 0/2] scheduler: expose the topology of clusters and
>> add cluster scheduler
>>
>> On 11/01/2021 10:28, Morten Rasmussen wrote:
>>> On Fri, Jan 08, 2021 at 12:22:41PM -0800, Tim Chen wrote:
>>>>
>>>>
>>>> On 1/8/21 7:12 AM, Morten Rasmussen wrote:
>>>>> On Thu, Jan 07, 2021 at 03:16:47PM -0800, Tim Chen wrote:
>>>>>> On 1/6/21 12:30 AM, Barry Song wrote:

[...]

>> wake_wide() switches between packing (select_idle_sibling(), llc_size
>> CPUs) and spreading (find_idlest_cpu(), all CPUs).
>>
>> AFAICS, since none of the sched domains set SD_BALANCE_WAKE, currently
>> all wakeups are (llc-)packed.
> 
> Sorry for late response. I was struggling with some other topology
> issues recently.
> 
> For "all wakeups are (llc-)packed",
> it seems you mean current want_affine is only affecting the new_cpu,
> and for wake-up path, we will always go to select_idle_sibling() rather
> than find_idlest_cpu() since nobody sets SD_WAKE_BALANCE in any
> sched_domain ?
> 
>>
>>  select_task_rq_fair()
>>
>>    for_each_domain(cpu, tmp)
>>
>>      if (tmp->flags & sd_flag)
>>        sd = tmp;
>>
>>
>> In case we would like to further distinguish between llc-packing and
>> even narrower (cluster or MC-L2)-packing, we would introduce a 2. level
>> packing vs. spreading heuristic further down in sis().
> 
> I didn't get your point on "2 level packing". Would you like
> to describe more? It seems you mean we need to have separate
> calculation for avg_scan_cost and sched_feat(SIS_) for cluster
> (or MC-L2) since cluster and llc are not in the same level
> physically?

By '1. level packing' I meant going sis() (i.e. sd=per_cpu(sd_llc,
target)) instead of routing WF_TTWU through find_idlest_cpu() which uses
a broader sd span (in case all sd's (or at least up to an sd > llc)
would have SD_BALANCE_WAKE set).
wake_wide() (wakee/waker flip heuristic) is currently used to make this
decision. But since no sd sets SD_BALANCE_WAKE we always go sis() for
WF_TTWU.

'2. level packing' would be the decision between cluster- and
llc-packing. The question was which heuristic could be used here.

>> IMHO, Barry's current implementation doesn't do this right now. Instead
>> he's trying to pack on cluster first and if not successful look further
>> among the remaining llc CPUs for an idle CPU.
> 
> Yes. That is exactly what the current patch is doing.

And this will be favoring cluster- over llc-packing for each task instead.

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-06  8:30 Barry Song
2021-01-06  8:30 ` [RFC PATCH v3 1/2] topology: Represent clusters of CPUs within a die Barry Song
2021-02-09 22:48   ` Masayoshi Mizuma
2021-01-06  8:30 ` [RFC PATCH v3 2/2] scheduler: add scheduler level for clusters Barry Song
2021-01-06 16:29   ` Vincent Guittot
2021-01-06 20:09     ` Song Bao Hua (Barry Song)
2021-01-07 23:16 ` [RFC PATCH v3 0/2] scheduler: expose the topology of clusters and add cluster scheduler Tim Chen
2021-01-08 15:12   ` Morten Rasmussen
2021-01-08 20:22     ` Tim Chen
2021-01-11  9:28       ` Morten Rasmussen
2021-01-12 11:00         ` Dietmar Eggemann
2021-01-25 10:50           ` Song Bao Hua (Barry Song)
2021-01-26 11:02             ` Dietmar Eggemann [this message]
2021-04-13 10:45           ` Song Bao Hua (Barry Song)
2021-04-13 19:00             ` Tim Chen
2021-01-08 21:30     ` Song Bao Hua (Barry Song)
2021-01-12 12:53       ` Dietmar Eggemann
2021-01-25 11:12         ` Song Bao Hua (Barry Song)
2021-02-03 11:32   ` Song Bao Hua (Barry Song)
2021-02-16 18:04     ` Tim Chen

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