Messages in this thread | | | From | Brice Goglin <> | Subject | AMD Bulldozer topology regression since 4.6 | Date | Tue, 29 Nov 2016 08:03:15 +0100 |
| |
Hello
Since Linux 4.6 (and still in 4.9-rc5 at least), both AMD Bulldozer cores of a single dual-core compute unit report the same core_id:
$ cat /sys/devices/system/cpu/cpu{?,??}/topology/core_id 0 0 1 1 2 2 3 0 3 [...]
Before 4.5 (and for a very long time), the kernel reported different core_ids:
0 1 2 3 4 5 6 7 0 [...]
This causes user-space tools (at least all that rely on hwloc for topology discovery) to think the processor has dual-threaded cores instead of dual-core compute-unit modules.
The cause is likely this patch, which seems to assume both cores of a same compute-unit have the same ID, which is wrong?
commit 8196dab4fc159943df6baaac04973bb1accb7100 Author: Borislav Petkov <bp@suse.de> Date: Fri Mar 25 15:52:36 2016 +0100
x86/cpu: Get rid of compute_unit_id It is cpu_core_id anyway. Signed-off-by: Borislav Petkov <bp@suse.de> Link: http://lkml.kernel.org/r/1458917557-8757-3-git-send-email-bp@alien8.de Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Thanks Brice
| |