linux-kernel - Re: [PATCH v2]: fix Haswell precise store data source encoding

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Date:	Thu, 15 May 2014 15:56:55 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	acme@...stprotocols.net, jolsa@...hat.com, jmario@...hat.com,
	ak@...ux.intel.com
Subject: Re: [PATCH v2]: fix Haswell precise store data source encoding

On Thu, May 15, 2014 at 05:56:44PM +0200, Stephane Eranian wrote:
> 
> This patch fixes a bug in  precise_store_data_hsw() whereby
> it would set the data source memory level to the wrong value.
> 
> As per the the SDM Vol 3b Table 18-41 (Layout of Data Linear
> Address Information in PEBS Record), when status bit 0 is set
> this is a L1 hit, otherwise this is a L1 miss.
> 
> This patch encodes the memory level according to the specification.
> 
> In V2, we added the filtering on the store events.
> Only the following events produce L1 information:
>  * MEM_UOPS_RETIRED.STLB_MISS_STORES
>  * MEM_UOPS_RETIRED.LOCK_STORES
>  * MEM_UOPS_RETIRED.SPLIT_STORES
>  * MEM_UOPS_RETIRED.ALL_STORES

This worked great on our Haswell-EX box.  I was a little surprised to find
out it did until I realized on Ivy Bridge 'mem-store' was a 0x02cd but on
Haswell it is now a 0x82d0.  Go generic event types! :-)

Looking at the SDM documentation it does say something about
'UOPS_RETIRED.ALL' supporting stores too but can't find that event.  Is
that a typo, much like the 0x02 umask for stores on the D0 event is
missing from the documentation?  Just wanted to make sure we are not
missing one more case.

Thanks for the quick patch Stephane!

Tested-and-Reviewed-by: Don Zickus <dzickus@...hat.com>

> 
> Signed-off-by: Stephane Eranian <eranian@...gle.com>
> 
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> index ae96cfa..980970c 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> @@ -108,15 +108,31 @@ static u64 precise_store_data(u64 status)
>  	return val;
>  }
>  
> -static u64 precise_store_data_hsw(u64 status)
> +static u64 precise_store_data_hsw(struct perf_event *event, u64 status)
>  {
>  	union perf_mem_data_src dse;
> +	u64 cfg = event->hw.config & INTEL_ARCH_EVENT_MASK;
>  
>  	dse.val = 0;
>  	dse.mem_op = PERF_MEM_OP_STORE;
>  	dse.mem_lvl = PERF_MEM_LVL_NA;
> +
> +	/*
> +	 * L1 info only valid for following events:
> +	 *
> +	 * MEM_UOPS_RETIRED.STLB_MISS_STORES
> +	 * MEM_UOPS_RETIRED.LOCK_STORES
> +	 * MEM_UOPS_RETIRED.SPLIT_STORES
> +	 * MEM_UOPS_RETIRED.ALL_STORES
> +	 */
> +	if (cfg != 0x12d0 && cfg != 0x22d0 && cfg != 0x42d0 && cfg != 0x82d0)
> +		return dse.mem_lvl;
> +
>  	if (status & 1)
> -		dse.mem_lvl = PERF_MEM_LVL_L1;
> +		dse.mem_lvl = PERF_MEM_LVL_L1 | PERF_MEM_LVL_HIT;
> +	else
> +		dse.mem_lvl = PERF_MEM_LVL_L1 | PERF_MEM_LVL_MISS;
> +
>  	/* Nothing else supported. Sorry. */
>  	return dse.val;
>  }
> @@ -887,7 +903,7 @@ static void __intel_pmu_pebs_event(struct perf_event *event,
>  				data.data_src.val = load_latency_data(pebs->dse);
>  			else if (event->hw.flags & PERF_X86_EVENT_PEBS_ST_HSW)
>  				data.data_src.val =
> -					precise_store_data_hsw(pebs->dse);
> +					precise_store_data_hsw(event, pebs->dse);
>  			else
>  				data.data_src.val = precise_store_data(pebs->dse);
>  		}
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