Messages in this thread | | | Subject | Re: [PATCH] perf, x86: Disable perf if the BIOS got its grubby paws on the PMU | From | Peter Zijlstra <> | Date | Fri, 03 Sep 2010 16:46:03 +0200 |
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On Fri, 2010-09-03 at 09:32 -0500, Matt Domsch wrote: > On Fri, Sep 03, 2010 at 06:53:59AM -0700, Arjan van de Ven wrote: > > On 9/3/2010 2:13 AM, Peter Zijlstra wrote: > > > > > >+static void print_BIOS_fail(void) > > >+{ > > >+ printk(KERN_ERR "\n"); > > >+ printk(KERN_ERR "=============================================\n"); > > >+ printk(KERN_ERR "It appears the BIOS is actively using the PMU\n"); > > >+ printk(KERN_ERR "this avoids Linux from using it, please de- \n"); > > >+ printk(KERN_ERR "activate this BIOS feature or request a BIOS \n"); > > >+ printk(KERN_ERR "update from your vendor. \n"); > > >+ printk(KERN_ERR "=============================================\n"); > > >+ > > >+ memset(&x86_pmu, 0, sizeof(x86_pmu)); > > >+}
> I must object to messages that repeatedly (at least on every boot) > tell system administrators to contact their hardware vendor's support > lines, when it's not clear what the BIOS is doing is incorrect.
It is using the PMU, it should not _ever_ do that.
> There > are plenty of valid reasons why BIOS itself would use PMU counters. > Dell PowerEdge server power management, handled by the BIOS, certainly > does use one.
Them make them stop doing that, or at least provide a BIOS option to disable this Feat^WFailure-add.
An no, doing power-management from the BIOS is most certainly not a valid reason. That's not what BIOSes are for, a BIOS should bring up the system and then sod off.
> My understanding is that there is a mechanism for the OS to request > BIOS to release use of PMU counters. Are we doing that?
I'm not aware of any such thing. The Intel Arch docs most certainly don't specify anything about that.
> If BIOS does > not release the counters when asked, ok, that's something to > (potentially) warn about. But blanket "BIOS is using a CPU feature! > Bad BIOS! No treat for you!" - that's not helpful to anyone.
Again, I'm not aware there is a spec on how to ask anything of the BIOS, let alone a part pertaining to PMU functionality.
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