On 09/26/2016 07:57 AM, Borislav Petkov wrote: > On Mon, Sep 26, 2016 at 07:45:37AM -0400, Prarit Bhargava wrote: >> When offline, /sys/devices/system/cpuX/cpu/online is 0. The problem is that >> when online is 0, topology disappears so there is no way to determine _the >> location_ of the offline'd thread. > > What does "the location" mean exactly? > >> cpupower should still print out all asterisks for down'd threads. It does >> not >> because the topology directory is incorrectly removed. >> >> IOW how does userspace know the _location_ of the thread? The topology >> directory no longer exists when the thread is downed, so core_id and >> physical_package_id (both of which would be effectively static) do not exist. >> The whole point of this patchset is to know where the offline'd thread >> actually is. > > What do you mean "where"?
The socket and core location. Look at it this way (and let's get the terminology straight at the same time). You have a socket CPU. That socket has cores on it. Each core (at least on Intel) has two threads. I down a thread (as you did): > > $ echo 0 > /sys/devices/system/cpu/cpu2/online This results in the topology directory being destroyed. It shouldn't be -- the socket and core are still there. If you could open up your computer you could touch them. This is similar to downing a PCI device, or removing !kernel memory DIMM from a system. The device is still physically there. > $ cat /sys/devices/system/cpu/online > 0-1,3-7 > > So core 2 is right between 1 and 3. Yes. But *where* is it relative to the cores and socket(s)? > > If you need to show the package id, you still iterate over the core > numbers in an increasing order and show '*' for the offlined ones. > Explain this in more detail please? P.
