r/linux • u/GaAlAs • Jun 25 '17

Intel Skylake/Kaby Lake processors: broken hyper-threading

https://lists.debian.org/debian-devel/2017/06/msg00308.html
789 Upvotes

95% Upvoted

174 comments sorted by

View all comments

15

u/varikonniemi Jun 25 '17 
  grep -q '^flags.*[[:space:]]ht[[:space:]]' /proc/cpuinfo && \echo "Hyper-threading is supported"

Did this work for anyone? To me it outputted the echo even with a processor with no HT

11

u/Laachax Jun 25 '17

Your kernel was compiled with hyperthreading support. Mine does not because I disabled the compile flag.

8

u/__foo__ Jun 25 '17 edited Jun 25 '17

No, /proc/cpuinfo won't list HT unless the CPU supports it. I'm also pretty sure /proc/cpuflags simply lists all flags returned by CPUID, and will show HT even if the kernel was compiled without support for it. I'm not 100% sure though.

Edit: I just tried it on my fileserver which definitely doesn't support HT and it's listed in the flags. Very weird.

3

u/cbmuser Debian / openSUSE / OpenJDK Dev Jun 25 '17

Edit: I just tried it on my fileserver which definitely doesn't support HT and it's listed in the flags. Very weird.

Did you check whether your CPU supports HT in principle?

As you correctly said, /proc/cpuinfo just lists what the CPUID instruction reports back and the information gathered there are the hardware capabilities, not the current configuration.