Messages in this thread | | | Date | Wed, 27 Mar 2019 10:56:42 +0000 | From | Quentin Perret <> | Subject | Re: [PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only |
| |
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
| |