linux-kernel - Re: 50 Watt idle power regression bisected to Linux-3.10

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Date:	Wed, 11 Dec 2013 13:43:52 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Galbraith <bitbucket@...ine.de>
Cc:	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Len Brown <lenb@...nel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jeremy Eder <jeder@...hat.com>, x86@...nel.org
Subject: Re: 50 Watt idle power regression bisected to Linux-3.10

On Wed, Dec 11, 2013 at 01:29:15PM +0100, Mike Galbraith wrote:
> On Wed, 2013-12-11 at 12:52 +0100, Peter Zijlstra wrote: 
> > On Wed, Dec 11, 2013 at 12:38:39PM +0100, Borislav Petkov wrote:
> > > Right, if it turns out that this is really the case and that this
> > > erratum hasn't been fixed for models later than 29 - we'd need the
> > > additional model numbers to set X86_FEATURE_CLFLUSH_MONITOR correctly.
> > 
> > You also need: https://lkml.org/lkml/2013/11/19/143
> > 
> > Because obviously not all mwait idle loops check that cpu bit.
> 
> I had tried that patch, to see if it would magically make the thing
> start working, nope.  I had also tried...

> +		if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
> +			clflush((void *)&current_thread_info()->flags);

Yeah, you need a bit extra to enable that feature bit for your CPU as
bpetkov said.

Something like the below.. someone needs to double check and possibly
add SNB/IVB EX parts if they're already available.

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index dc1ec0dff939..015642eed045 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -387,8 +387,15 @@ static void init_intel(struct cpuinfo_x86 *c)
 			set_cpu_cap(c, X86_FEATURE_PEBS);
 	}
 
-	if (c->x86 == 6 && c->x86_model == 29 && cpu_has_clflush)
-		set_cpu_cap(c, X86_FEATURE_CLFLUSH_MONITOR);
+	if (c->x86 == 6 && cpu_has_clflush) {
+		switch (c->x86_model) {
+		case 29: /* Core2 EX */
+		case 46: /* NHM EX */
+		case 47: /* WSM EX */
+			set_cpu_cap(c, X86_FEATURE_CLFLUSH_MONITOR);
+			break;
+		}
+	}
 
 #ifdef CONFIG_X86_64
 	if (c->x86 == 15)
--
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