Messages in this thread Patch in this message | | | Date | Tue, 26 Mar 2019 13:03:48 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH] cpu/hotplug: Create SMT sysfs interface for all arches |
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On Tue, Mar 26, 2019 at 02:53:04PM +0100, Thomas Gleixner wrote: > On Tue, 26 Mar 2019, Josh Poimboeuf wrote: > > On Sun, Mar 24, 2019 at 09:13:18PM +0100, Thomas Gleixner wrote: > > > Second thoughts. I'm not really convinced that changing the meaning of > > > notsupported and in fact overloading it, is the right thing to do. > > > notsupported means now: > > > > > > CPU does not support it - OR - architecture does not support it > > > > > > That's not pretty and we are surely not short of state space. There are > > > several options for handling this: > > > > > > 1) Do not expose the state file, just expose the active file > > > > > > 2) Expose the state file, but return -ENOTSUPP or some other sensible error > > > code > > > > > > 3) Expose the state file and let show return 'notimplemented' which is > > > more accurate. That wouldn't even require to expand the state space > > > enum. It just can be returned unconditionally. > > > > Makes sense. I like #3. I can post another version. > > Yes, please.
Something like so (on top of the original patch)?
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 4a11cba73085..5eea46fefcb2 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -511,11 +511,12 @@ Description: Control Symetric Multi Threading (SMT) 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" Runtime SMT toggling is not currently - supported for the architecture + "on" SMT is enabled + "off" SMT is disabled + "forceoff" SMT is force disabled. Cannot be changed. + "notsupported" SMT is not supported by the CPU + "notimplemented" SMT runtime toggling is not + implemented for the architecture If control status is "forceoff" or "notsupported" writes are rejected. diff --git a/kernel/cpu.c b/kernel/cpu.c index 517ab1803a22..05a71ee98440 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2145,7 +2145,11 @@ static const char *smt_states[] = { static ssize_t show_smt_control(struct device *dev, struct device_attribute *attr, char *buf) { - return snprintf(buf, PAGE_SIZE - 2, "%s\n", smt_states[cpu_smt_control]); + const char *state = IS_ENABLED(CONFIG_HOTPLUG_SMT) ? + smt_states[cpu_smt_control] : + "notimplemented"; + + return snprintf(buf, PAGE_SIZE - 2, "%s\n", state); } static ssize_t
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