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authorNysal Jan K.A <nysal@linux.ibm.com>2024-07-31 08:31:12 +0530
committerMichael Ellerman <mpe@ellerman.id.au>2024-08-13 10:31:24 +1000
commit6c17ea1f3eaa330d445ac14a9428402ce4e3055e (patch)
tree4e5e903107d323ebe0ea0be31f8e1f0fce17f5ad /Documentation/ABI
parente7e846dc6c73fbc94ae8b4ec20d05627646416f2 (diff)
cpu/SMT: Enable SMT only if a core is online
If a core is offline then enabling SMT should not online CPUs of this core. By enabling SMT, what is intended is either changing the SMT value from "off" to "on" or setting the SMT level (threads per core) from a lower to higher value. On PowerPC the ppc64_cpu utility can be used, among other things, to perform the following functions: ppc64_cpu --cores-on # Get the number of online cores ppc64_cpu --cores-on=X # Put exactly X cores online ppc64_cpu --offline-cores=X[,Y,...] # Put specified cores offline ppc64_cpu --smt={on|off|value} # Enable, disable or change SMT level If the user has decided to offline certain cores, enabling SMT should not online CPUs in those cores. This patch fixes the issue and changes the behaviour as described, by introducing an arch specific function topology_is_core_online(). It is currently implemented only for PowerPC. Fixes: 73c58e7e1412 ("powerpc: Add HOTPLUG_SMT support") Reported-by: Tyrel Datwyler <tyreld@linux.ibm.com> Closes: https://groups.google.com/g/powerpc-utils-devel/c/wrwVzAAnRlI/m/5KJSoqP4BAAJ Signed-off-by: Nysal Jan K.A <nysal@linux.ibm.com> Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20240731030126.956210-2-nysal@linux.ibm.com
Diffstat (limited to 'Documentation/ABI')
-rw-r--r--Documentation/ABI/testing/sysfs-devices-system-cpu3
1 files changed, 2 insertions, 1 deletions
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 325873385b71..de725ca3be82 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -562,7 +562,8 @@ Description: Control Symmetric Multi Threading (SMT)
================ =========================================
If control status is "forceoff" or "notsupported" writes
- are rejected.
+ are rejected. Note that enabling SMT on PowerPC skips
+ offline cores.
What: /sys/devices/system/cpu/cpuX/power/energy_perf_bias
Date: March 2019