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

["Liang, Kan" <kan.liang@linux.intel.com>]

On 4/8/2022 3:53 PM, 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.

It sounds similar to the Forward state. Why can't the 
PERF_MEM_SNOOPX_FWD be reused?

Thanks,
Kan

> 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@amazon.com>
> ---
>   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 */