diff mbox series

[v2,01/15] perf/x86/lbr: Simplify the exposure check for the LBR_INFO registers

Message ID 20221125040604.5051-2-weijiang.yang@intel.com
State New
Headers
Series Introduce Architectural LBR for vPMU |

Commit Message

Yang, Weijiang Nov. 25, 2022, 4:05 a.m. UTC 
  From: Like Xu <like.xu@linux.intel.com>

The x86_pmu.lbr_info is 0 unless explicitly initialized, so there's
no point checking x86_pmu.intel_cap.lbr_format.

Cc: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Like Xu <like.xu@linux.intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
 arch/x86/events/intel/lbr.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

Comments

Like Xu Dec. 22, 2022, 10:57 a.m. UTC | #1 
Hi Peter, would you help apply this one in your tip/perf tree,
as it doesn't seem to be closely tied to the KVM changes. Thanks.

On 25/11/2022 12:05 pm, Yang Weijiang wrote:
> From: Like Xu <like.xu@linux.intel.com>
> 
> The x86_pmu.lbr_info is 0 unless explicitly initialized, so there's
> no point checking x86_pmu.intel_cap.lbr_format.
> 
> Cc: Peter Zijlstra <peterz@infradead.org>
> Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Signed-off-by: Like Xu <like.xu@linux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
>   arch/x86/events/intel/lbr.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
> index 4dbde69c423b..e7caabfa1377 100644
> --- a/arch/x86/events/intel/lbr.c
> +++ b/arch/x86/events/intel/lbr.c
> @@ -1606,12 +1606,10 @@ void __init intel_pmu_arch_lbr_init(void)
>    */
>   void x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
>   {
> -	int lbr_fmt = x86_pmu.intel_cap.lbr_format;
> -
>   	lbr->nr = x86_pmu.lbr_nr;
>   	lbr->from = x86_pmu.lbr_from;
>   	lbr->to = x86_pmu.lbr_to;
> -	lbr->info = (lbr_fmt == LBR_FORMAT_INFO) ? x86_pmu.lbr_info : 0;
> +	lbr->info = x86_pmu.lbr_info;
>   }
>   EXPORT_SYMBOL_GPL(x86_perf_get_lbr);
>
Peter Zijlstra Dec. 22, 2022, 1:29 p.m. UTC | #2 
On Thu, Dec 22, 2022 at 06:57:50PM +0800, Like Xu wrote:
> Hi Peter, would you help apply this one in your tip/perf tree,
> as it doesn't seem to be closely tied to the KVM changes. Thanks.

OK, I'll go queue it for perf/core after -rc1
Sean Christopherson Dec. 22, 2022, 5:41 p.m. UTC | #3 
On Thu, Dec 22, 2022, Like Xu wrote:
> Hi Peter, would you help apply this one in your tip/perf tree,
> as it doesn't seem to be closely tied to the KVM changes. Thanks.
> 
> On 25/11/2022 12:05 pm, Yang Weijiang wrote:
> > From: Like Xu <like.xu@linux.intel.com>
> > 
> > The x86_pmu.lbr_info is 0 unless explicitly initialized, so there's
> > no point checking x86_pmu.intel_cap.lbr_format.
> > 
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
> > Reviewed-by: Andi Kleen <ak@linux.intel.com>
> > Signed-off-by: Like Xu <like.xu@linux.intel.com>
> > Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> > ---
> >   arch/x86/events/intel/lbr.c | 4 +---
> >   1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
> > index 4dbde69c423b..e7caabfa1377 100644
> > --- a/arch/x86/events/intel/lbr.c
> > +++ b/arch/x86/events/intel/lbr.c
> > @@ -1606,12 +1606,10 @@ void __init intel_pmu_arch_lbr_init(void)
> >    */
> >   void x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
> >   {
> > -	int lbr_fmt = x86_pmu.intel_cap.lbr_format;
> > -
> >   	lbr->nr = x86_pmu.lbr_nr;
> >   	lbr->from = x86_pmu.lbr_from;
> >   	lbr->to = x86_pmu.lbr_to;
> > -	lbr->info = (lbr_fmt == LBR_FORMAT_INFO) ? x86_pmu.lbr_info : 0;
> > +	lbr->info = x86_pmu.lbr_info;

This stable-worthy a bug fix, no?  E.g. won't the existing code misreport lbr->info
if the format is LBR_FORMAT_INFO2?

> >   }
> >   EXPORT_SYMBOL_GPL(x86_perf_get_lbr);
Like Xu Dec. 23, 2022, 2:12 a.m. UTC | #4 
On 23/12/2022 1:41 am, Sean Christopherson wrote:
> On Thu, Dec 22, 2022, Like Xu wrote:
>> Hi Peter, would you help apply this one in your tip/perf tree,
>> as it doesn't seem to be closely tied to the KVM changes. Thanks.
>>
>> On 25/11/2022 12:05 pm, Yang Weijiang wrote:
>>> From: Like Xu <like.xu@linux.intel.com>
>>>
>>> The x86_pmu.lbr_info is 0 unless explicitly initialized, so there's
>>> no point checking x86_pmu.intel_cap.lbr_format.
>>>
>>> Cc: Peter Zijlstra <peterz@infradead.org>
>>> Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
>>> Reviewed-by: Andi Kleen <ak@linux.intel.com>
>>> Signed-off-by: Like Xu <like.xu@linux.intel.com>
>>> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
>>> ---
>>>    arch/x86/events/intel/lbr.c | 4 +---
>>>    1 file changed, 1 insertion(+), 3 deletions(-)
>>>
>>> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
>>> index 4dbde69c423b..e7caabfa1377 100644
>>> --- a/arch/x86/events/intel/lbr.c
>>> +++ b/arch/x86/events/intel/lbr.c
>>> @@ -1606,12 +1606,10 @@ void __init intel_pmu_arch_lbr_init(void)
>>>     */
>>>    void x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
>>>    {
>>> -	int lbr_fmt = x86_pmu.intel_cap.lbr_format;
>>> -
>>>    	lbr->nr = x86_pmu.lbr_nr;
>>>    	lbr->from = x86_pmu.lbr_from;
>>>    	lbr->to = x86_pmu.lbr_to;
>>> -	lbr->info = (lbr_fmt == LBR_FORMAT_INFO) ? x86_pmu.lbr_info : 0;
>>> +	lbr->info = x86_pmu.lbr_info;
> 
> This stable-worthy a bug fix, no?  E.g. won't the existing code misreport lbr->info
> if the format is LBR_FORMAT_INFO2?

Sure, we need "Cc: stable@vger.kernel.org" in order not to lose misprediction 
and cycles
information on the LBR_FORMAT_INFO2 platforms like Goldmont plus.

> 
>>>    }
>>>    EXPORT_SYMBOL_GPL(x86_perf_get_lbr);
diff mbox series

Patch

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index 4dbde69c423b..e7caabfa1377 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -1606,12 +1606,10 @@  void __init intel_pmu_arch_lbr_init(void)
  */
 void x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
 {
-	int lbr_fmt = x86_pmu.intel_cap.lbr_format;
-
 	lbr->nr = x86_pmu.lbr_nr;
 	lbr->from = x86_pmu.lbr_from;
 	lbr->to = x86_pmu.lbr_to;
-	lbr->info = (lbr_fmt == LBR_FORMAT_INFO) ? x86_pmu.lbr_info : 0;
+	lbr->info = x86_pmu.lbr_info;
 }
 EXPORT_SYMBOL_GPL(x86_perf_get_lbr);