linux-kernel - Re: [PATCH v5 2/5] perf: Add SNOOP_PEER flag to perf mem data struct

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Message-ID: <20220420082040.GA843168@leoy-ThinkPad-X240s>
Date:   Wed, 20 Apr 2022 16:20:40 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Ali Saidi <alisaidi@...zon.com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, german.gomez@....com,
        acme@...nel.org, benh@...nel.crashing.org, Nick.Forrington@....com,
        alexander.shishkin@...ux.intel.com, andrew.kilroy@....com,
        james.clark@....com, john.garry@...wei.com, jolsa@...nel.org,
        kjain@...ux.ibm.com, lihuafei1@...wei.com, mark.rutland@....com,
        mathieu.poirier@...aro.org, mingo@...hat.com, namhyung@...nel.org,
        peterz@...radead.org, will@...nel.org
Subject: Re: [PATCH v5 2/5] perf: Add SNOOP_PEER flag to perf mem data struct

On Fri, Apr 08, 2022 at 07:53:41PM +0000, Ali Saidi wrote:
> Add a flag to the perf mem data struct to signal that a request caused a
> cache-to-cache transfer of a line from a peer of the requestor and
> wasn't sourced from a lower cache level.  The line being moved from one
> peer cache to another has latency and performance implications. On Arm64
> Neoverse systems the data source can indicate a cache-to-cache transfer
> but not if the line is dirty or clean, so instead of overloading HITM
> define a new flag that indicates this type of transfer.
> 
> Signed-off-by: Ali Saidi <alisaidi@...zon.com>

The patch looks good to me:
Reviewed-by: Leo Yan <leo.yan@...aro.org>

Sine this is a common flag, it's better if x86 or PowerPC maintainers
could take a look for this new snooping type.  Thanks!

Leo

> ---
>  include/uapi/linux/perf_event.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 82858b697c05..c9e58c79f3e5 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -1308,7 +1308,7 @@ union perf_mem_data_src {
>  #define PERF_MEM_SNOOP_SHIFT	19
>  
>  #define PERF_MEM_SNOOPX_FWD	0x01 /* forward */
> -/* 1 free */
> +#define PERF_MEM_SNOOPX_PEER	0x02 /* xfer from peer */
>  #define PERF_MEM_SNOOPX_SHIFT  38
>  
>  /* locked instruction */
> -- 
> 2.32.0
>