On Wed, Sep 21, 2016 at 09:32:47AM -0400, Prarit Bhargava wrote:
> This is not the right thing to do . The topology directory should exist as
> long as the thread is present in the system. The thread (and its core) are
> still physically there, it's just that the thread is not available to the
> scheduler. The topology of the thread hasn't changed due to it being soft
> offlined this way.
So far so good.
> turbostat was modified to deal with the missing topology directory, and in
> utility cpupower prints out significantly less information when a thread is
Why does it do that? Why does an offlined core change that info?
Concrete details please.
> ISTR a powertop bug due to hotplug too. This makes these monitoring
> utilities a problem for users who want only one thread per core.
one thread per core? What does that mean?
> This now means that
> echo 0 > /sys/devices/system/cpu/cpu29/online
> will result in the thread's topology directory staying around until the struct
> device associated with it is destroyed upon a physical socket hotplug event.
So your 2/2 says that on an offlined CPU, you have
and this information is bollocks. core_siblings is 0, thread_siblings
is 0. You can just as well not have them there at all.
So is this whole jumping around just so that you can have a
/sys/devices/system/cpu/cpu10/topology directory and so that tools don't
get confused by it missing?
So again, what exactly are those tools accessing and how does the
offlined cores puzzle them?
A concrete example please:
"turbostat tries to access X and it is gone when the CPU is offlined so
this is a problem because it can't do Y"
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