linux-kernel - Re: perf hw in kexeced kernel broken in tip

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Date:	Thu, 9 Dec 2010 23:44:27 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Jason Wessel <jason.wessel@...driver.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Haren Myneni <hbabu@...ibm.com>
Subject: Re: perf hw  in kexeced kernel broken in tip

On Thu, Dec 09, 2010 at 03:20:08PM -0500, Don Zickus wrote:
...
> 
> Getting closer...
> 
> Pentium4s are special they need the double write, so...
> 
> > +	/*
> > +	 * Now write a value and read it back to see if it matches,
> > +	 * this is needed to detect certain hardware emulators (qemu/kvm)
> > +	 * that don't trap on the MSR access and always return 0s.
> > +	 */
> >  	val = 0xabcdUL;
> > -	ret |= checking_wrmsrl(x86_pmu.perfctr, val);
> > +	ret = checking_wrmsrl(x86_pmu.perfctr, val);
> 
> 	if (x86_pmu.perfctr_second_write)
> 		ret |= checking_wrmsrl(x86_pmu.perfctr, val);
> 
> solved my p4 problems for kexec.
> 
...

yeah, thanks! would you push a patch upstream?

  Cyrill
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