Messages in this thread | | | Date | Tue, 16 Jul 2013 11:45:16 +0530 | Subject | Re: [PATCH 7/8] cpufreq: Preserve policy structure across suspend/resume | From | Viresh Kumar <> |
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On 15 July 2013 15:35, Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> wrote: > Actually even I was wondering about this while writing the patch and > I even tested shutdown after multiple suspend/resume cycles, to verify that > the refcount is messed up. But surprisingly, things worked just fine. > > Logically there should've been a refcount mismatch and things should have > failed, but everything worked fine during my tests. Apart from suspend/resume > and shutdown tests, I even tried mixing a few regular CPU hotplug operations > (echo 0/1 to sysfs online files), but nothing stood out. > > Sorry, I forgot to document this in the patch. Either the patch is wrong > or something else is silently fixing this up. Not sure what is the exact > situation.
To understand it I actually applied your patches to get better view of the code. (Haven't tested it though).. And found that your code is doing the right thing and we shouldn't get a mismatch.. This is the sequence of events I can draw:
- __cpu_add_dev() for first cpu. sets the refcount to 'x', where x are the no. of cpus in its clock domain. - _cpu_add_dev() for other cpus: doesn't change anything in refcount
- Suspend: - cpu_remove_dev() for all cpus, due to frozen flag we don't touch the value of count - Resume: - cpu_add_dev() for all cpus, due to frozen flag we don't touch the value of count.
And so things work as expected. That's why your code isn't breaking anything I believe.
But can no. of cpus change inbetween suspend/resume? Then count would be tricky as we are using the same policy structure.
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