Re: [PATCH RFC] x86: avoid atomic operation in test_and_set_bit_lock if possible

Ingo Molnar
2011-03-25T09:59:59Z

* Eric Dumazet <eric.dumazet@gmail.com> wrote:

> Le vendredi 25 mars 2011 à 10:32 +0100, Ingo Molnar a écrit :
> > * Eric Dumazet <eric.dumazet@gmail.com> wrote:
> >
> > > Le vendredi 25 mars 2011 à 00:56 +0100, Andi Kleen a écrit :
> > > > > never EVER seen any good explanation of why that particular sh*t
> > > > > argument would b true. It seems to be purely about politics, where
> > > > > some idiotic vendor (namely HP) has convinced Intel that they really
> > > > > need it. To the point where some engineers seem to have bought into
> > > > > the whole thing and actually believe that fairy tale ("firmware can do
> > > > > better" - hah! They must be feeding people some bad drugs at the
> > > > > cafeteria)
> > > >
> > > > For the record I don't think it's a good idea for the BIOS to do
> > > > this (and I'm not aware of any engineer who does),
> > > > but I think Linux should do better than just disabling PMU use when
> > > > this happens.
> > > >
> > > > However I suspect taking over SCI would cause endless problems
> > > > and is very likely not a good idea.
> > >
> > > I tried many different changes in BIOS and all failed (the machine is
> > > damn slow at boot, this takes age).
> > >
> > > I am stuck :(
> >
> > Could you please try the patch below?
>
> This obviously works, [...]

Congrats to your now much-improved perf experience! :-)

> [...] but you probably need to make a full pass to make sure we dont have a
> MSR failure -this should return false in this case.

Wanted to keep this patch simple - we are not really hitting MSR failure cases
in practice, and by getting the message the user is at least warned that
*something* is amiss.

Thanks,

Ingo