From: Andrew Lunn <andrew@lunn.ch>
To: David Jander <david@protonic.nl>
Cc: Mark Brown <broonie@kernel.org>,
Marc Kleine-Budde <mkl@pengutronix.de>,
linux-spi@vger.kernel.org, Oleksij Rempel <ore@pengutronix.de>
Subject: Re: [RFC] A new SPI API for fast, low-latency regmap peripheral access
Date: Thu, 19 May 2022 17:21:59 +0200 [thread overview]
Message-ID: <YoZgl5xMmt+SCS2L@lunn.ch> (raw)
In-Reply-To: <20220519163327.606295d2@erd992>
> Since I am already moving the stats to per-cpu structs, wouldn't atomic_inc()
> be sufficient and even faster for uint32 stats on 32bit systems?
atomic is expensive, because it needs to synchronise across all
CPUs. And that synchoniszation across all CPUs is pointless when you
are doing per-cpu counters.
> I still would like to hear Mark's idea on the exact types. All bytes stats
> were ULL and transfer counter values were UL. Possibly the reason behind this
> was to make the transfer counters as efficient to increment as possible for
> the given platform, as should be the case for "unsigned long".
That efficiency argument is however broken by the use of a spinlock,
which is much more expensive than the actually increment. Except for a
UP machine when it becomes a NOP. But UP machines are becoming less
and less common.
Andrew
next prev parent reply other threads:[~2022-05-19 15:22 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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YoZgl5xMmt+SCS2L@lunn.ch \
--to=andrew@lunn.ch \
--cc=broonie@kernel.org \
--cc=david@protonic.nl \
--cc=linux-spi@vger.kernel.org \
--cc=mkl@pengutronix.de \
--cc=ore@pengutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).