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

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Date: Wed, 14 Feb 2024 07:42:57 +0000
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: Mark Brown <broonie@...nel.org>
Cc: Théo Lebrun <theo.lebrun@...tlin.com>,
 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 15:28, Mark Brown wrote:
> On Tue, Feb 13, 2024 at 12:39:02PM +0000, Tudor Ambarus wrote:
>> On 2/9/24 13:51, Théo Lebrun wrote:
> 
>>> +		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.
> 
> If we can cope with this sort of statistics collection in the networking
> fast path we can probably cope with it for SPI too, the immediate
> recording is all per CPU so I'd like to see some numbers showing that
> it's a problem before worrying about it too much.  Even the people doing
> things like saturating CAN buses haven't been raising it as a concern
> for the regular SPI data path.  We could add a Kconfig if it's an issue.

Ok, we can deal with it afterwards if it'll become an issue.