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Message-ID: <20190329162651.GA9608@kroah.com>
Date: Fri, 29 Mar 2019 17:26:51 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Lingutla Chandrasekhar <clingutla@...eaurora.org>
Cc: quentin.perret@....com, sudeep.holla@....com,
dietmar.eggemann@....com, juri.lelli@...il.com,
catalin.marinas@....com, jeremy.linton@....com,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] arch_topology: Make cpu_capacity sysfs node as
ready-only
On Thu, Mar 28, 2019 at 10:17:05AM +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 hotplugged 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 asymmetry 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@....com>
> Tested-by: Quentin Perret <quentin.perret@....com>
> Reviewed-by: Quentin Perret <quentin.perret@....com>
> Acked-by: Sudeep Holla <sudeep.holla@....com>
> Signed-off-by: Lingutla Chandrasekhar <clingutla@...eaurora.org>
I see 3 "v2" patches in my queue, all different :(
Also, you need to list what changed below the --- line as the
documentation says to do so. Please fix up and resend v3.
thanks,
greg k-h
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