Viresh Kumar wrote:
On 12 February 2015 at 11:03, Saravana Kannan skannan@codeaurora.org wrote:
gov = find_governor(per_cpu(cpufreq_cpu_governor,policy->cpu));
gov = find_governor(policy->last_governor);Just change this to:
gov = policy->governor;
No need to search for the governor again. It should already be valid for policy that's being restored. For new policies, it would be NULL and would get defaulted correctly.
No. Apart from the fact that one of my patches is making it NULL intentionally, here are the problems that I see with reusing the pointer:
- All CPUs of a policy are down
- The last used governor is removed (was built in as a module)
- Now if we online the CPUs again, it wouldn't work as the pointer
insn't usable.
- Or if we insert the governor again, pointers would change and then
onlining the CPUs wouldn't work..
I think for logical hotplug we should lock the governor from being removed. Or, if you don't want that, go set the pointer to NULL lazily when/if that happens.
- For physical hotplug of CPUs, the policies are getting freed (I
assume and hope so). So, the "last_governor" field is going to be empty.
Its not about it being empty. Its more about when we don't remove them physically..
- Even if we continue storing the last_governor outside of the policy,
for physical hotplug of CPUs where the policy is getting recreated, I'm not sure restoring the governor is the right thing to do anyway. I'll explain various possible configurations below for the physical hotplug case:
We do it today as this is part of the per-cpu stuff now and my patch would fix it then :)
I'm not sure if you read rest of my email. Unless you added some patches recently, restoring the last_governor is definitely functionally broken as of at least 3.12. Probably 3.14 too (I need to check again). It just restores the governor with the default tunables. So, it's kinda useless in the real world. You might as well set it to default governor because it's just as helpful as using the last governor with different tunables.
-Saravana