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From: Andrew Lunn <andrew@lunn.ch>
To: David Jander <david@protonic.nl>
Cc: linux-spi@vger.kernel.org, Mark Brown <broonie@kernel.org>,
	Marc Kleine-Budde <mkl@pengutronix.de>,
	Oleksij Rempel <ore@pengutronix.de>
Subject: Re: [RFC] A new SPI API for fast, low-latency regmap peripheral access
Date: Fri, 13 May 2022 14:10:32 +0200	[thread overview]
Message-ID: <Yn5KuOF7aH6xEAH0@lunn.ch> (raw)
In-Reply-To: <20220512163445.6dcca126@erd992>

> 6.1. Accounting spinlocks:
> 
> Spinlocks are supposed to be fast, especially for the case that they are not
> contested, but in such critical paths their impact shouldn't be neglected.
> 
> SPI_STATISTICS_ADD_TO_FIELD: This macro defined in spi.h has a spinlock, and
> it is used 4 times directly in __spi_sync(). It is also used in
> spi_transfer_one_message() which is called from there. Removing the spinlocks
> (thus introducing races) makes the code measurably faster (several us).
> 
> spi_statistics_add_transfer_stats(): Called twice from
> spi_transfer_one_message(), and also contains a spinlock. Removing these again
> has a measurable impact of several us.

Maybe something from the network stack can be learnt here:

https://www.kernel.org/doc/html/latest/locking/seqlock.html

https://elixir.bootlin.com/linux/v5.18-rc6/source/include/linux/u64_stats_sync.h

	Andrew

      parent reply	other threads:[~2022-05-13 12:10 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-12 14:34 [RFC] A new SPI API for fast, low-latency regmap peripheral access David Jander
2022-05-12 20:37 ` Mark Brown
2022-05-12 22:12   ` Mark Brown
2022-05-13 12:46   ` David Jander
2022-05-13 19:36     ` Mark Brown
2022-05-16 16:28       ` Marc Kleine-Budde
2022-05-16 17:46         ` Mark Brown
2022-05-17 10:24           ` David Jander
2022-05-17 11:57             ` Mark Brown
2022-05-17 13:09               ` David Jander
2022-05-17 13:43                 ` Mark Brown
2022-05-17 15:16                   ` David Jander
2022-05-17 18:17                     ` Mark Brown
2022-05-19  8:12                       ` David Jander
2022-05-19  8:24                         ` Marc Kleine-Budde
2022-05-19 12:14                         ` Andrew Lunn
2022-05-19 14:33                           ` David Jander
2022-05-19 15:21                             ` Andrew Lunn
2022-05-20 15:22                         ` Mark Brown
2022-05-23 14:48                           ` David Jander
2022-05-23 14:59                             ` Marc Kleine-Budde
2022-05-24 11:30                               ` David Jander
2022-05-24 19:46                                 ` Mark Brown
2022-05-25 14:39                                   ` David Jander
2022-05-13 12:10 ` Andrew Lunn [this message]

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