| Message ID | 1571740391-3251-2-git-send-email-ego@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | pseries/hotplug: Change the default behaviour of cede_offline | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/apply_patch | success | Successfully applied on branch powerpc/merge (6b450d0404ca83dc131dadffd40c5aa6f7a603af) |
| snowpatch_ozlabs/build-ppc64le | success | Build succeeded |
| snowpatch_ozlabs/build-ppc64be | success | Build succeeded |
| snowpatch_ozlabs/build-ppc64e | success | Build succeeded |
| snowpatch_ozlabs/build-pmac32 | success | Build succeeded |
| snowpatch_ozlabs/checkpatch | success | total: 0 errors, 0 warnings, 0 checks, 26 lines checked |
"Gautham R. Shenoy" <ego@linux.vnet.ibm.com> writes: > From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com> > > Currently on PSeries Linux guests, the offlined CPU can be put to one > of the following two states: > - Long term processor cede (also called extended cede) > - Returned to the hypervisor via RTAS "stop-self" call. > > This is controlled by the kernel boot parameter "cede_offline=on/off". > > By default the offlined CPUs enter extended cede. The PHYP hypervisor > considers CPUs in extended cede to be "active" since they are still > under the control fo the Linux guests. Hence, when we change the SMT > modes by offlining the secondary CPUs, the PURR and the RWMR SPRs will > continue to count the values for offlined CPUs in extended cede as if > they are online. This breaks the accounting in tools such as lparstat. > > To fix this, ensure that by default the offlined CPUs are returned to > the hypervisor via RTAS "stop-self" call by changing the default value > of "cede_offline_enabled" to false. > > Fixes: commit 3aa565f53c39 ("powerpc/pseries: Add hooks to put the CPU > into an appropriate offline state") > > Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> I'm OK with changing the default as a precursor to removing the code that implements the cede offline mode. Acked-by: Nathan Lynch <nathanl@linux.ibm.com>
diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst index 4a50ab7..5319593 100644 --- a/Documentation/core-api/cpu_hotplug.rst +++ b/Documentation/core-api/cpu_hotplug.rst @@ -53,7 +53,7 @@ Command Line Switches ``cede_offline={"off","on"}`` Use this option to disable/enable putting offlined processors to an extended ``H_CEDE`` state on supported pseries platforms. If nothing is specified, - ``cede_offline`` is set to "on". + ``cede_offline`` is set to "off". This option is limited to the PowerPC architecture. diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c index bbda646..f9d0366 100644 --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c @@ -46,7 +46,17 @@ static DEFINE_PER_CPU(enum cpu_state_vals, preferred_offline_state) = static enum cpu_state_vals default_offline_state = CPU_STATE_OFFLINE; -static bool cede_offline_enabled __read_mostly = true; +/* + * Determines whether the offlined CPUs should be put to a long term + * processor cede (called extended cede) for power-saving + * purposes. The CPUs in extended cede are still with the Linux Guest + * and are not returned to the Hypervisor. + * + * By default, the offlined CPUs are returned to the hypervisor via + * RTAS "stop-self". This behaviour can be changed by passing the + * kernel commandline parameter "cede_offline=on". + */ +static bool cede_offline_enabled __read_mostly; /* * Enable/disable cede_offline when available.