linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Fri, 19 Dec 2014 12:46:16 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>, Chris Mason <clm@...com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Suresh Siddha <sbsiddha@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Anvin <hpa@...ux.intel.com>
Subject: Re: frequent lockups in 3.18rc4

On Fri, Dec 19, 2014 at 11:51 AM, Linus Torvalds
<torvalds@...ux-foundation.org> 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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