Re: [PATCH] x86: Add a turbo mode sysctl

On Sat, 2 Apr 2016, Andy Lutomirski wrote:

On Fri, Apr 1, 2016 at 9:10 AM, Thomas Gleixner [off-list ref] wrote:

quoted

quoted

+     if (turbo_mode)
+             write_cr0(cr0 & ~X86_CR0_CD);
+     else
+             write_cr0(cr0 | X86_CR0_CD);

I think proper turbo mode disable requires ~(X86_CR0_CD | X86_CR0_NW)

I thought that made no difference on family 6 and P4 and was actively
dangerous (disabled coherency) before.  At least, that's what the
table of caching modes and the footnote seems to say.

CD=0 and NW=1 result in #GP, which might be your intent as that is definitely
the slowest mode you can achieve. But you should add a comment at least.

I think we should merge this patch and add a special-case so that
calling unlink on turbo_mode sets it to zero.  Then people who rm -rf
/ will brick their systems more slowly :)

While at it can you please make a turbo = 0 call when we hit a WARN/BUG/Panic
so the messages spill slower over the screen?

Thanks,

	tglx