On 10/06/2013 02:10 AM, Ingo Molnar wrote:
>>
>> I'm wanting to hear from the x86 people on why we have this absurd knob
>> to begin with; but I'm tempted to simply disable all of perf if you
>> touch it.
>
> I'm fully with you, please zap the 'notsc' boot option - it's an ancient
> relic, if any box is still broken with the TSC on we want to hear about it
> and fix it!
>
Perhaps better would be to make the notsc option do what other feature
removal options do and just remove the CPU feature flag.
Early on we had a bunch of ad hoc behaviors for feature disabling. They
are harmful and just wrong... "not present" and "disabled" should be the
same thing in 99% of all cases (in the case of the TSC one may wish to
set the CR4 bit which disables the TSC from userspace, but I don't think
"notsc" ever did that.)
However:
pr_warn("Kernel compiled with CONFIG_X86_TSC, cannot disable TSC
completely\n");
That is a total "say what"?
At one point it even said:
printk(KERN_WARNING "notsc: Kernel compiled with CONFIG_X86_TSC, "
"cannot disable TSC.\n");
CONFIG_X86_TSC is a baseline control option; we shouldn't key
functionality off of it. It's fine to say notsc -> no tracing, but
making it a compile-time key makes me a bit uphappy. We cut off 386,
but cutting of 486 at this point makes me nervous.
-hpa
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