Messages in this thread | | | Date | Tue, 22 Sep 2015 09:14:59 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v2 1/2] x86/msr: Carry on after a non-"safe" MSR access fails without !panic_on_oops |
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* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Mon, Sep 21, 2015 at 1:46 AM, Ingo Molnar <mingo@kernel.org> wrote: > > > > Linus, what's your preference? > > So quite frankly, is there any reason we don't just implement > native_read_msr() as just > > unsigned long long native_read_msr(unsigned int msr) > { > int err; > unsigned long long val; > > val = native_read_msr_safe(msr, &err); > WARN_ON_ONCE(err); > return val; > } > > Note: no inline, no nothing. Just put it in arch/x86/lib/msr.c, and be > done with it. I don't see the downside.
Absolutely!
> How many msr reads are <i>so</i> critical that the function call overhead would > matter? Get rid of the inline version of the _safe() thing too, and put that > thing there too.
Only a very low number of them is performance critical (because even hw-accelerated MSR accesses are generally slow so we try to avoid MSR accesses in fast paths as much as possible, via shadowing, etc.) - and in the few cases where we have to access an MSR in a fast path we can do those separately.
I'm only worried about the 'default' APIs, i.e. rdmsr() that is used throughout arch/x86/ over a hundred times, not about performance critical code paths that get enough testing and enough attention in general.
Thanks,
Ingo
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