linux-kernel - Re: [PATCH 06/13] perf_events: disable LBR support for older Intel Atom processors (v3)

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Date:	Fri, 27 Jan 2012 11:13:50 +0530
From:	Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	acme@...radead.org, robert.richter@....com, ming.m.lin@...el.com,
	andi@...stfloor.org, asharma@...com, ravitillo@....gov,
	vweaver1@...s.utk.edu
Subject: Re: [PATCH 06/13] perf_events: disable LBR support for older Intel
 Atom processors (v3)

On Monday 09 January 2012 10:19 PM, Stephane Eranian wrote:
> The patch adds a restriction for Intel Atom LBR support. Only
> steppings 10 (PineView) and more recent are supported. Older models,
> do not have a functional LBR. Their LBR does not freeze on PMU interrupt
> which makes LBR unusable in the context of perf_events.
> 
> Signed-off-by: Stephane Eranian <eranian@...gle.com>
  Reviewed-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
> ---
>  arch/x86/kernel/cpu/perf_event_intel_lbr.c |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> index 8a1eb6c..e2b7094 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> @@ -313,6 +313,16 @@ void intel_pmu_lbr_init_snb(void)
>  /* atom */
>  void intel_pmu_lbr_init_atom(void)
>  {
> +	/*
> +	 * only models starting at stepping 10 seems
> +	 * to have an operational LBR which can freeze
> +	 * on PMU interrupt
> +	 */
> +	if (boot_cpu_data.x86_mask < 10) {
> +		pr_cont("LBR disabled due to erratum");
> +		return;
> +	}
> +
>  	x86_pmu.lbr_nr	   = 8;
>  	x86_pmu.lbr_tos    = MSR_LBR_TOS;
>  	x86_pmu.lbr_from   = MSR_LBR_CORE_FROM;


-- 
Linux Technology Centre
IBM Systems and Technology Group
Bangalore India

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