Messages in this thread | | | Date | Tue, 18 Nov 2014 00:38:14 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH v3 13/13] perf/x86: add syfs entry to disable HT bug workaround |
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On Tue, 18 Nov 2014, Borislav Petkov wrote: > On Mon, Nov 17, 2014 at 08:07:05PM +0100, Stephane Eranian wrote: > > From: Maria Dimakopoulou <maria.n.dimakopoulou@gmail.com> > > > > This patch adds a sysfs entry: > > > > /sys/devices/cpu/ht_bug_workaround > > > > to activate/deactivate the PMU HT bug workaround. > > > > To activate (activated by default): > > # echo 1 > /sys/devices/cpu/ht_bug_workaround > > > > To deactivate: > > # echo 0 > /sys/devices/cpu/ht_bug_workaround > > If I put my simple-user hat and stare at this sysfs node, I'm not really > becoming any smarter from looking at the name. HT bug? A hyper-threading > bug?? I see the user forums going nuts already. > > Instead of adding a sysfs node per CPU bug, I'm wondering whether adding > a > > /sys/devices/system/cpu/bugs > > file which gets a mask of bits to enable and disable workarounds would > be much cleaner. > > x86 guys, what do you guys think?
Well a bitmask is a pretty indescriptive item as well. Putting my user hat on: Where is the documentation for the bits?
> Such a scheme should be much more easily extensible in the future in > case we want to add another workaround toggle.
Agreed, but that does not make it more intuitive.
> The hierarchy is not optimal either as it should be under > "perf"-something but I don't think we have a perf sysfs node...
I'm not sure about that. Its a CPU bug at the very end. We should not care much which of the various bits and pieces of a CPU it affects and some of them affect more than one ....
But OTOH, we dont want to have random entries with impossible to understand file names under /sys/devices/cpu/ either.
So what about adding:
/sys/devices/cpu/bugs/ and collect the various user tweakable (or not) bug data there.
So for the problem at hand:
/sys/devices/cpu/bugs/ht_some_sensible_name/
Directory
/sys/devices/cpu/bugs/ht_some_sensible_name/info
File, which describes the bug comprehensive. URL reference, Errata Nr. or something like that.
/sys/devices/cpu/bugs/ht_some_sensible_name/workaround
File, to retrieve the status of the workaround. Possibly RO depending on the nature of the issue.
> > static DEVICE_ATTR(rdpmc, S_IRUSR | S_IWUSR, get_attr_rdpmc, set_attr_rdpmc); > > +static DEVICE_ATTR(ht_bug_workaround, S_IRUSR | S_IWUSR, get_attr_xsu, > > + set_attr_xsu); > > > > static struct attribute *x86_pmu_attrs[] = { > > &dev_attr_rdpmc.attr, > > + &dev_attr_ht_bug_workaround.attr, > > You should be adding this dynamically, only when running on Intel, i.e. > > if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) > /* add bug_workaround attr */
and if it's a family/model specific issue, we don't want to see it if we are not running on such a machine. > For an example, see amd_l3_attrs() in > arch/x86/kernel/cpu/intel_cacheinfo.c
Given the fact that the number of bugs is going to grow, we probably want some infrastructure for this.
Thanks,
tglx
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