[cfarm-users] Temporarily disabling SMT

[Alexander Kruppa]

Hello,

would it be possible to allow users to disable SMT (a.k.a. hyperthreading)
temporarily on one cpu core? This would be useful for doing timing runs
that are not affected by other processes running on another logical cpu on
the same physical core.

This can be accomplished by taking all but one logical cpu on a physical
core offline via
/sys/devices/system/cpu/cpu*/online
For example, on gcc121,
$ head /sys/devices/system/cpu/cpu??/topology/thread_siblings_list | tail
-n 2
==> /sys/devices/system/cpu/cpu31/topology/thread_siblings_list <==
15,31
shows that logical cpus 15 and 31 are on the same physical core. With
# echo 0 > /sys/devices/system/cpu/cpu31/online
as root, logical cpu 31 can be taken offline, so that processes on logical
core 15 run effectively without SMT interference until logical core 31 is
put online again.

Is there any interest in allowing such a mechanism?

All the best,
Alex
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.tetaneutral.net/pipermail/cfarm-users/attachments/20201022/7b2ed838/attachment.html>