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 > distinction. >
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) wouldn't exist. 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. P.
