From: Julien Grall <julien.grall@arm.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: Juergen Gross <jgross@suse.com>, Peng Fan <peng.fan@nxp.com>,
Steve Capper <Steve.Capper@arm.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Dario Faggioli <dario.faggioli@citrix.com>,
Punit Agrawal <punit.agrawal@arm.com>,
George Dunlap <george.dunlap@citrix.com>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
Jan Beulich <jbeulich@suse.com>, Peng Fan <van.freenix@gmail.com>
Subject: Re: [RFC 0/5] xen/arm: support big.little SoC
Date: Thu, 22 Sep 2016 19:54:02 +0100 [thread overview]
Message-ID: <e47afc4e-0ce1-97a9-6abc-f4d33b4d7c24@arm.com> (raw)
In-Reply-To: <alpine.DEB.2.10.1609221028560.26423@sstabellini-ThinkPad-X260>
Hi Stefano,
On 22/09/2016 18:31, Stefano Stabellini wrote:
> On Thu, 22 Sep 2016, Julien Grall wrote:
>> Hello Peng,
>>
>> On 22/09/16 10:27, Peng Fan wrote:
>>> On Thu, Sep 22, 2016 at 10:50:23AM +0200, Dario Faggioli wrote:
>>>> On Thu, 2016-09-22 at 14:49 +0800, Peng Fan wrote:
>>>>> On Wed, Sep 21, 2016 at 08:11:43PM +0100, Julien Grall wrote:
>>>> A feature like `xl cpupool-biglittle-split' can still be interesting,
>>>
>>> "cpupool-cluster-split" maybe a better name?
>>
>> You seem to assume that a cluster, from the MPIDR point of view, can only
>> contain the same set of CPUs. I don't think this is part of the architecture,
>> so this may not be true in the future.
>
> Interesting. I also understood that a cluster can only have one kind if
> cpus. Honestly it would be a little insane for it to be otherwise :-)
I don't think this is insane (or maybe I am insane :)). Cluster usually
doesn't share all L2 cache (assuming L1 is local to each core) and L3
cache may not be present, so if you move a task from one cluster to
another you will add latency because the new L2 cache has to be refilled.
The use case of big.LITTLE is big cores are used for short period of
burst and little core are used for the rest (e.g listening audio,
fetching mail...). If you want to reduce latency when switch between big
and little CPUs, you may want to put them within the same cluster.
Also, as mentioned in another thread, you may have a platform with the
same micro-architecture (e.g Cortex A-53) but different silicon
implementation (e.g to have a different frequency, power efficiency).
Here the concept of big.LITTLE is more blurred.
That's why I am quite reluctant to name (even if it may be more handy to
the user) "big" and "little" the different CPU set.
Cheers,
--
Julien Grall
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next prev parent reply other threads:[~2016-09-22 18:54 UTC|newest]
Thread overview: 85+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-19 2:08 [RFC 0/5] xen/arm: support big.little SoC van.freenix
2016-09-19 2:08 ` [RFC 1/5] xen/arm: domain_build: setting opt_dom0_max_vcpus according to cpupool0 info van.freenix
2016-09-19 2:08 ` [RFC 2/5] xen: cpupool: introduce cpupool_arch_info van.freenix
2016-09-19 2:08 ` [RFC 3/5] xen: cpupool: add arch cpupool hook van.freenix
2016-09-19 2:08 ` [RFC 4/5] xen/arm: move vpidr from arch_domain to arch_vcpu van.freenix
2016-09-19 2:08 ` [RFC 5/5] xen/arm: cpupool: implement arch_domain_cpupool_compatible van.freenix
2016-09-19 8:09 ` [RFC 0/5] xen/arm: support big.little SoC Julien Grall
2016-09-19 8:36 ` Peng Fan
2016-09-19 8:53 ` Julien Grall
2016-09-19 9:38 ` Peng Fan
2016-09-19 9:59 ` Julien Grall
2016-09-19 13:15 ` Peng Fan
2016-09-19 20:56 ` Stefano Stabellini
2016-09-19 9:45 ` George Dunlap
2016-09-19 10:06 ` Julien Grall
2016-09-19 10:23 ` Juergen Gross
2016-09-19 17:18 ` Dario Faggioli
2016-09-19 21:03 ` Stefano Stabellini
2016-09-19 22:55 ` Dario Faggioli
2016-09-20 0:01 ` Stefano Stabellini
2016-09-20 0:54 ` Dario Faggioli
2016-09-20 10:03 ` Peng Fan
2016-09-20 10:27 ` George Dunlap
2016-09-20 15:34 ` Julien Grall
2016-09-20 17:24 ` Dario Faggioli
2016-09-20 19:09 ` Stefano Stabellini
2016-09-20 19:41 ` Julien Grall
2016-09-20 20:17 ` Stefano Stabellini
2016-09-21 8:38 ` Peng Fan
2016-09-21 9:22 ` George Dunlap
2016-09-21 12:35 ` Peng Fan
2016-09-21 15:00 ` Dario Faggioli
2016-09-21 10:15 ` Julien Grall
2016-09-21 12:28 ` Peng Fan
2016-09-21 15:06 ` Dario Faggioli
2016-09-22 9:45 ` Peng Fan
2016-09-22 11:21 ` Julien Grall
2016-09-23 2:38 ` Peng Fan
2016-09-21 10:09 ` Julien Grall
2016-09-21 10:22 ` George Dunlap
2016-09-21 13:06 ` Julien Grall
2016-09-21 15:45 ` Dario Faggioli
2016-09-21 19:28 ` Julien Grall
2016-09-22 6:16 ` Peng Fan
2016-09-22 8:43 ` Dario Faggioli
2016-09-22 11:24 ` Julien Grall
2016-09-22 16:31 ` Dario Faggioli
2016-09-23 13:56 ` Julien Grall
2016-09-21 18:13 ` Stefano Stabellini
2016-09-21 19:11 ` Julien Grall
2016-09-21 19:21 ` Julien Grall
2016-09-21 23:45 ` Stefano Stabellini
2016-09-22 6:49 ` Peng Fan
2016-09-22 8:50 ` Dario Faggioli
2016-09-22 9:27 ` Peng Fan
2016-09-22 9:51 ` George Dunlap
2016-09-22 10:09 ` Peng Fan
2016-09-22 10:39 ` Dario Faggioli
2016-09-22 10:13 ` Juergen Gross
2016-09-22 9:52 ` Dario Faggioli
2016-09-22 11:29 ` Julien Grall
2016-09-22 17:31 ` Stefano Stabellini
2016-09-22 18:54 ` Julien Grall [this message]
2016-09-23 2:14 ` Peng Fan
2016-09-23 9:24 ` Julien Grall
2016-09-23 10:05 ` Peng Fan
2016-09-23 10:15 ` Julien Grall
2016-09-23 13:36 ` Dario Faggioli
2016-09-24 1:57 ` Stefano Stabellini
2016-09-23 13:52 ` Dario Faggioli
2016-09-24 1:35 ` Stefano Stabellini
2016-09-23 2:03 ` Peng Fan
2016-09-22 10:05 ` Peng Fan
2016-09-22 16:26 ` Dario Faggioli
2016-09-22 17:33 ` Stefano Stabellini
2016-09-21 12:38 ` Peng Fan
2016-09-21 9:45 ` Dario Faggioli
2016-09-20 10:18 ` George Dunlap
2016-09-19 20:55 ` Stefano Stabellini
2016-09-19 10:33 ` George Dunlap
2016-09-19 13:33 ` Peng Fan
2016-09-20 0:11 ` Dario Faggioli
2016-09-20 6:18 ` Peng Fan
2016-09-19 16:43 ` Dario Faggioli
2016-09-19 13:08 ` Peng Fan
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