From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
Andrea Arcangeli <aarcange@redhat.com>,
Waiman Long <longman@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Jiri Kosina <jikos@kernel.org>
Subject: Re: [PATCH] cpu/hotplug: Create SMT sysfs interface for all arches
Date: Tue, 26 Mar 2019 08:32:36 -0500 [thread overview]
Message-ID: <20190326133236.lylrrbacznezybjm@treble> (raw)
In-Reply-To: <alpine.DEB.2.21.1903242104280.1798@nanos.tec.linutronix.de>
On Sun, Mar 24, 2019 at 09:13:18PM +0100, Thomas Gleixner wrote:
> On Fri, 1 Mar 2019, Josh Poimboeuf wrote:
> > Make the /sys/devices/system/cpu/smt/* files available on all arches, so
> > user space has a consistent way to detect whether SMT is enabled.
> >
> > The 'control' file now shows 'notsupported' for architectures which
> > don't yet have CONFIG_HOTPLUG_SMT.
>
> I'm slowly crawling through my backlog ...
>
> > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > @@ -514,7 +514,8 @@ Description: Control Symetric Multi Threading (SMT)
> > "on" SMT is enabled
> > "off" SMT is disabled
> > "forceoff" SMT is force disabled. Cannot be changed.
> > - "notsupported" SMT is not supported by the CPU
> > + "notsupported" Runtime SMT toggling is not currently
> > + supported for the architecture
>
> 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.
--
Josh
next prev parent reply other threads:[~2019-03-26 13:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-01 17:42 [PATCH] cpu/hotplug: Create SMT sysfs interface for all arches Josh Poimboeuf
2019-03-06 15:44 ` Thomas Gleixner
2019-03-24 20:13 ` Thomas Gleixner
2019-03-26 13:32 ` Josh Poimboeuf [this message]
2019-03-26 13:53 ` Thomas Gleixner
2019-03-26 18:03 ` Josh Poimboeuf
2019-03-26 18:34 ` Thomas Gleixner
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