Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <a96681b5-5532-470e-17d1-afe4c8d195ad@linux.intel.com>
Date:   Wed, 20 Apr 2022 14:43:28 -0400
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
 Thunderbird/91.8.0
Subject: Re: [PATCH v5 2/5] perf: Add SNOOP_PEER flag to perf mem data struct
Content-Language: en-US
To:     Ali Saidi <alisaidi@amazon.com>, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, german.gomez@arm.com,
        leo.yan@linaro.org, acme@kernel.org
Cc:     benh@kernel.crashing.org, Nick.Forrington@arm.com,
        alexander.shishkin@linux.intel.com, andrew.kilroy@arm.com,
        james.clark@arm.com, john.garry@huawei.com, jolsa@kernel.org,
        kjain@linux.ibm.com, lihuafei1@huawei.com, mark.rutland@arm.com,
        mathieu.poirier@linaro.org, mingo@redhat.com, namhyung@kernel.org,
        peterz@infradead.org, will@kernel.org
References: <20220408195344.32764-1-alisaidi@amazon.com>
 <20220408195344.32764-3-alisaidi@amazon.com>
From:   "Liang, Kan" <kan.liang@linux.intel.com>
In-Reply-To: <20220408195344.32764-3-alisaidi@amazon.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


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 */