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
