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| author | Thomas Gleixner <tglx@linutronix.de> | 2018-05-29 18:48:27 +0300 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2018-06-21 15:20:58 +0300 |
| commit | 05736e4ac13c08a4a9b1ef2de26dd31a32cbee57 (patch) | |
| tree | dbd83041b6208c02967f398cbf32f8cfd1b83db7 /Documentation/ABI | |
| parent | cc1fe215e1efa406b03aa4389e6269b61342dec5 (diff) | |
| download | linux-05736e4ac13c08a4a9b1ef2de26dd31a32cbee57.tar.xz | |
cpu/hotplug: Provide knobs to control SMT
Provide a command line and a sysfs knob to control SMT.
The command line options are:
'nosmt': Enumerate secondary threads, but do not online them
'nosmt=force': Ignore secondary threads completely during enumeration
via MP table and ACPI/MADT.
The sysfs control file has the following states (read/write):
'on': SMT is enabled. Secondary threads can be freely onlined
'off': SMT is disabled. Secondary threads, even if enumerated
cannot be onlined
'forceoff': SMT is permanentely disabled. Writes to the control
file are rejected.
'notsupported': SMT is not supported by the CPU
The command line option 'nosmt' sets the sysfs control to 'off'. This
can be changed to 'on' to reenable SMT during runtime.
The command line option 'nosmt=force' sets the sysfs control to
'forceoff'. This cannot be changed during runtime.
When SMT is 'on' and the control file is changed to 'off' then all online
secondary threads are offlined and attempts to online a secondary thread
later on are rejected.
When SMT is 'off' and the control file is changed to 'on' then secondary
threads can be onlined again. The 'off' -> 'on' transition does not
automatically online the secondary threads.
When the control file is set to 'forceoff', the behaviour is the same as
setting it to 'off', but the operation is irreversible and later writes to
the control file are rejected.
When the control status is 'notsupported' then writes to the control file
are rejected.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'Documentation/ABI')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-devices-system-cpu | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 9c5e7732d249..65d9b844ecfd 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -487,3 +487,23 @@ Description: Information about CPU vulnerabilities "Not affected" CPU is not affected by the vulnerability "Vulnerable" CPU is affected and no mitigation in effect "Mitigation: $M" CPU is affected and mitigation $M is in effect + +What: /sys/devices/system/cpu/smt + /sys/devices/system/cpu/smt/active + /sys/devices/system/cpu/smt/control +Date: June 2018 +Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org> +Description: Control Symetric Multi Threading (SMT) + + active: Tells whether SMT is active (enabled and siblings online) + + control: Read/write interface to control SMT. Possible + values: + + "on" SMT is enabled + "off" SMT is disabled + "forceoff" SMT is force disabled. Cannot be changed. + "notsupported" SMT is not supported by the CPU + + If control status is "forceoff" or "notsupported" writes + are rejected. |