Re: frequent lockups in 3.18rc4

[Linus Torvalds]

On Fri, Dec 19, 2014 at 11:51 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I do note that we depend on the "new mwait" semantics where we do
> mwait with interrupts disabled and a non-zero RCX value. Are there
> possibly even any known CPU errata in that area? Not that it sounds
> likely, but still..

Remind me what CPU you have in that machine again? The %rax value for
the mwait cases in question seems to be 0x32, which is either C7s-HSW
or C7s-BDW, and in both cases has the "TLB flushed" flag set.

I'm pretty sure you have a Haswell, I'm just checking. Which model?
I'm assuming it's family 6, model 60, stepping 3? I found you
mentioning i5-4670T in a perf thread.. That the one?

Anyway, I don't actually believe in any CPU bugs, but you could try
"intel_idle.max_cstate=0" and see if that makes any difference, for
example.

Or perhaps just "intel_idle.max_cstate=1", which leaves intel_idle
active, but gets rid of the deeper sleep states (that incidentally
also play games with leave_mm() etc)

                            Linus
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