Re: [PATCH 0/2 v3] cpu hotplug: Preserve topology directory after soft remove event
From: Prarit Bhargava
Date: Wed Sep 28 2016 - 06:06:57 EST
On 09/28/2016 02:48 AM, Peter Zijlstra wrote:
> On Tue, Sep 27, 2016 at 11:26:14AM -0400, Prarit Bhargava wrote:
>> I see now that the issue is not understanding the difference between physical
>> and soft thread removal. I will write that up and get back to everyone.
> You don't seem to understand that from the kernels POV there is no such
And I'm saying you're wrong. Unlike PCI, CPU sysfs unplug does not completely
remove the device from the kernel's knowledge. If that were the case then
/sys/devices/system/cpu/cpuX/online (and other files left after the unplug)
If you do a physical removal (signaled via ACPI or interrupt) the entire device
is removed from the kernel's POV.
Yes, the sysfs removal is a subset of the physical removal. But the end result
is very different.
> There is only one unplug operation that caters to both cases. Therefore
> unplug needs to assume the most stringent (ie. physical) for things to
> work right.
See last comment above.