linux-kernel - Re: [PATCH] spi: spi-mem: add statistics support to ->exec

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Date: Wed, 14 Feb 2024 08:00:06 +0000
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: Théo Lebrun <theo.lebrun@...tlin.com>,
 Mark Brown <broonie@...nel.org>
Cc: linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
 Dhruva Gole <d-gole@...com>, Gregory CLEMENT <gregory.clement@...tlin.com>,
 Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>
Subject: Re: [PATCH] spi: spi-mem: add statistics support to ->exec_op() calls



On 2/13/24 15:00, Théo Lebrun wrote:
> Hello Tudor,

Hi!

> 
> On Tue Feb 13, 2024 at 1:39 PM CET, Tudor Ambarus wrote:
>>>  /**
>>>   * 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.
> 
> I did my testing on a 40 MHz octal SPI NOR with most reads being much
> bigger than 256 bytes, so I probably didn't have the fastest setup
> indeed.

yeah, reads are bigger, the entire flash can be read with a single read op.

> 
> What shape would that take? A spi-mem DT prop? New field in the SPI
> statistics sysfs directory?
> 

I think I'd go with a sysfs entry, it provides flexibility. But I guess
we can worry about this if we have some numbers, and I don't have, so
you're fine even without the opt-out option.

> Other remarks have been taken into account, thanks!
> 

Ok, thanks.
Cheers,
ta