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Message-ID: <b0844e5a-ee4b-4608-99a1-877660e01d57@linaro.org>
Date: Tue, 13 Feb 2024 12:39:02 +0000
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Subject: Re: [PATCH] spi: spi-mem: add statistics support to ->exec_op() calls
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To: =?UTF-8?Q?Th=C3=A9o_Lebrun?= <theo.lebrun@bootlin.com>,
 Mark Brown <broonie@kernel.org>
Cc: linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org,
 Dhruva Gole <d-gole@ti.com>, Gregory CLEMENT <gregory.clement@bootlin.com>,
 Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>,
 Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
 Tawfik Bayouk <tawfik.bayouk@mobileye.com>
References: <20240209-spi-mem-stats-v1-1-dd1a422fc015@bootlin.com>
From: Tudor Ambarus <tudor.ambarus@linaro.org>
In-Reply-To: <20240209-spi-mem-stats-v1-1-dd1a422fc015@bootlin.com>
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On 2/9/24 13:51, Théo Lebrun wrote:
> Current behavior is that spi-mem operations do not increment statistics,
> neither per-controller nor per-device, if ->exec_op() is used. For
> operations that do NOT use ->exec_op(), stats are increased as the
> usual spi_sync() is called.
> 
> The newly implemented spi_mem_add_op_stats() function is strongly
> inspired by spi_statistics_add_transfer_stats(); locking logic and
> l2len computation comes from there.
> 
> Statistics that are being filled: bytes{,_rx,_tx}, messages, transfers,
> errors, timedout, transfer_bytes_histo_*.
> 
> Note about messages & transfers counters: in the fallback to spi_sync()
> case, there are from 1 to 4 transfers per message. We only register one
> big transfer in the ->exec_op() case as that is closer to reality.
> 
> This patch is NOT touching:
>  - spi_async, spi_sync, spi_sync_immediate: those counters describe
>    precise function calls, incrementing them would be lying. I believe
>    comparing the messages counter to spi_async+spi_sync is a good way
>    to detect ->exec_op() calls, but I might be missing edge cases
>    knowledge.
>  - transfers_split_maxsize: splitting cannot happen if ->exec_op() is
>    provided.
> 
> Testing this patch:
> 
>    $ cd /sys/devices/platform/soc
>    $ find . -type d -path "*spi*" -name statistics
>    ./2100000.spi/spi_master/spi0/statistics
>    ./2100000.spi/spi_master/spi0/spi0.0/statistics
>    $ cd ./2100000.spi/spi_master/spi0/statistics
> 
>    $ for f in *; do printf "%s\t" $f; cat $f; done | \
>          grep -v transfer_bytes_histo | column -t
>    bytes                    240745444
>    bytes_rx                 240170907
>    bytes_tx                 126320
>    errors                   0
>    messages                 97354
>    spi_async                0
>    spi_sync                 0
>    spi_sync_immediate       0
>    timedout                 0
>    transfers                97354
>    transfers_split_maxsize  0
> 
> Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
> ---
>  drivers/spi/spi-mem.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 49 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
> index 2dc8ceb85374..171fe6b1c247 100644
> --- a/drivers/spi/spi-mem.c
> +++ b/drivers/spi/spi-mem.c
> @@ -297,6 +297,50 @@ static void spi_mem_access_end(struct spi_mem *mem)
>  		pm_runtime_put(ctlr->dev.parent);
>  }
>  
> +static void spi_mem_add_op_stats(struct spi_statistics __percpu *pcpu_stats,
> +				 const struct spi_mem_op *op, int exec_op_ret)
> +{
> +	struct spi_statistics *stats;
> +	int len, l2len;
> +
> +	get_cpu();
> +	stats = this_cpu_ptr(pcpu_stats);
> +	u64_stats_update_begin(&stats->syncp);
> +
> +	/*
> +	 * We do not have the concept of messages or transfers. Let's consider
> +	 * that one operation is equivalent to one message and one transfer.
> +	 */
> +	u64_stats_inc(&stats->messages);
> +	u64_stats_inc(&stats->transfers);
> +
> +	/* Use the sum of all lengths as bytes count and histogram value. */
> +	len = (int)op->cmd.nbytes + (int)op->addr.nbytes;
> +	len += (int)op->dummy.nbytes + (int)op->data.nbytes;

spi_mem_check_op() makes sure that op->cmd.nbytes != 0, otherwise it
returns -EINVAL ...

> +	u64_stats_add(&stats->bytes, len);
> +	l2len = min(fls(len), SPI_STATISTICS_HISTO_SIZE) - 1;

.. thus l2len can never be negative. You can declare len and l2len as
u64. The casts from above shall disappear.

> +	l2len = max(l2len, 0);
> +	u64_stats_inc(&stats->transfer_bytes_histo[l2len]);
> +
> +	/* Only account for data bytes as xferred bytes. */

s/xferred/transferred?

> +	if (op->data.nbytes && op->data.dir == SPI_MEM_DATA_OUT)
> +		u64_stats_add(&stats->bytes_tx, op->data.nbytes);
> +	if (op->data.nbytes && op->data.dir == SPI_MEM_DATA_IN)
> +		u64_stats_add(&stats->bytes_rx, op->data.nbytes);
> +
> +	/*
> +	 * A timeout is not an error, following the same behavior as
> +	 * spi_transfer_one_message().
> +	 */
> +	if (exec_op_ret == -ETIMEDOUT)
> +		u64_stats_inc(&stats->timedout);
> +	else if (exec_op_ret)
> +		u64_stats_inc(&stats->errors);
> +
> +	u64_stats_update_end(&stats->syncp);
> +	put_cpu();
> +}
> +
>  /**
>   * spi_mem_exec_op() - Execute a memory operation
>   * @mem: the SPI memory
> @@ -339,8 +383,12 @@ int spi_mem_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
>  		 * read path) and expect the core to use the regular SPI
>  		 * interface in other cases.
>  		 */
> -		if (!ret || ret != -ENOTSUPP || ret != -EOPNOTSUPP)
> +		if (!ret || ret != -ENOTSUPP || ret != -EOPNOTSUPP) {
> +			spi_mem_add_op_stats(ctlr->pcpu_statistics, op, ret);
> +			spi_mem_add_op_stats(mem->spi->pcpu_statistics, op, ret);
> +

Would be good to be able to opt out the statistics if one wants it.

SPI NORs can write with a single write op maximum page_size bytes, which
is typically 256 bytes. And since there are SPI NORs that can run at 400
MHz, I guess some performance penalty shouldn't be excluded.

>  			return ret;
> +		}
>  	}
>  
>  	tmpbufsize = op->cmd.nbytes + op->addr.nbytes + op->dummy.nbytes;
> 
> ---
> base-commit: 19b50f80b3a4865bd477aa5c026dd234d39a50d2
> change-id: 20240209-spi-mem-stats-ff9bf91c0f7e
> 
> Best regards,