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From: Quentin Perret <quentin.perret@arm.com>
To: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Cc: sudeep.holla@arm.com, dietmar.eggemann@arm.com,
	gregkh@linuxfoundation.org, will.deacon@arm.com,
	catalin.marinas@arm.com, morten.rasmussen@arm.com,
	linux-arm-kernel@lists.infradead.org, jeremy.linton@arm.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only
Date: Wed, 27 Mar 2019 10:56:42 +0000	[thread overview]
Message-ID: <20190327105640.ibiw5mvuggp35msl@queper01-lin> (raw)
In-Reply-To: <1552048728-29657-1-git-send-email-clingutla@codeaurora.org>

Hi,

On Friday 08 Mar 2019 at 18:08:48 (+0530), Lingutla Chandrasekhar wrote:
> If user updates any cpu's cpu_capacity, then the new value is going to
> be applied to all its online sibling cpus. But this need not to be correct
> always, as sibling cpus (in ARM, same micro architecture cpus) would have
> different cpu_capacity with different performance characteristics.
> So updating the user supplied cpu_capacity to all cpu siblings
> is not correct.
> 
> And another problem is, current code assumes that 'all cpus in a cluster
> or with same package_id (core_siblings), would have same cpu_capacity'.
> But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove
> cpu topology sibling masks")', when a cpu hotplugged out, the cpu
> information gets cleared in its sibling cpus. So user supplied
> cpu_capacity would be applied to only online sibling cpus at the time.
> After that, if any cpu hot plugged in, it would have different cpu_capacity
> than its siblings, which breaks the above assumption.
> 
> So instead of mucking around the core sibling mask for user supplied
> value, use device-tree to set cpu capacity. And make the cpu_capacity
> node as read-only to know the assymetry between cpus in the system.
> While at it, remove cpu_scale_mutex usage, which used for sysfs write
> protection.
> 
> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Acked-by: Sudeep Holla <sudeep.holla@arm.com>
> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>

Reviewed-by: Quentin Perret <quentin.perret@arm.com>
Tested-by: Quentin Perret <quentin.perret@arm.com>

Thanks for doing this,
Quentin

  reply	other threads:[~2019-03-27 10:56 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20190306152254.GB19434@e105550-lin.cambridge.arm.com>
2019-03-06 15:27 ` [PATCH v1] arch_topology: Make cpu_capacity sysfs node as ready-only Lingutla Chandrasekhar
2019-03-07  7:28   ` Juri Lelli
2019-03-07  9:31     ` Quentin Perret
2019-03-07  9:57       ` Juri Lelli
2019-03-07 12:14         ` Quentin Perret
2019-03-07 15:04           ` Sudeep Holla
2019-03-07 15:19   ` Sudeep Holla
2019-03-08 11:45   ` Dietmar Eggemann
2019-03-08 12:38     ` [PATCH v2] " Lingutla Chandrasekhar
2019-03-27 10:56       ` Quentin Perret [this message]
2019-03-27 11:57 Lingutla Chandrasekhar
2019-03-27 16:15 ` Mukesh Ojha
2019-03-28  4:47 Lingutla Chandrasekhar
2019-03-28  6:56 ` Mukesh Ojha
2019-03-29 16:26 ` Greg KH

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