From: Mark Brown <broonie@kernel.org>
To: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: "linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Fabio Estevam <festevam@gmail.com>,
Rasmus Villemoes <Rasmus.Villemoes@prevas.se>
Subject: Re: [RFC PATCH 0/4] spi: spi-fsl-spi: try to make cpu-mode transfers faster
Date: Tue, 2 Apr 2019 16:10:05 +0700 [thread overview]
Message-ID: <20190402091005.GC2059@sirena.org.uk> (raw)
In-Reply-To: <ce9e8ca8-6db7-1be8-5ea3-c098b1c1c813@prevas.dk>
[-- Attachment #1: Type: text/plain, Size: 858 bytes --]
On Tue, Apr 02, 2019 at 08:43:51AM +0000, Rasmus Villemoes wrote:
> Thanks! There's one other option I can think of: don't do the interrupts
> at all, but just busy-wait for the completion of each word transfer (in
> a cpu_relax() loop). That could be guarded by something like
> 1000000*bits_per_word < hz (roughly, the word transfer takes less than 1
> us). At least on -rt, having the interrupt thread scheduled in and out
> again easily takes more than 1us of cpu time, and AFAIU we'd still be
> preemptible throughout - and/or one can throw in a cond_resched() every
> nnn words. But this might be a bit -rt specific, and the 1us threshold
> is rather arbitrary.
Yeah, that's definitely worth exploring as a mitigation but obviously
with things like flash I/O that gets a bit rude. Hopefully what's there
at the minute turns out to be robust enough.
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
prev parent reply other threads:[~2019-04-02 9:10 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-27 14:30 [RFC PATCH 0/4] spi: spi-fsl-spi: try to make cpu-mode transfers faster Rasmus Villemoes
2019-03-27 14:30 ` [RFC PATCH 1/4] spi: spi-fsl-spi: remove always-true conditional in fsl_spi_do_one_msg Rasmus Villemoes
2019-04-01 8:54 ` Applied "spi: spi-fsl-spi: remove always-true conditional in fsl_spi_do_one_msg" to the spi tree Mark Brown
2019-03-27 14:30 ` [RFC PATCH 3/4] spi: spi-fsl-spi: allow changing bits_per_word while CS is still active Rasmus Villemoes
2019-03-27 14:30 ` [RFC PATCH 2/4] spi: spi-fsl-spi: relax message sanity checking a little Rasmus Villemoes
2019-04-01 8:54 ` Applied "spi: spi-fsl-spi: relax message sanity checking a little" to the spi tree Mark Brown
2019-03-27 14:30 ` [RFC PATCH 4/4] spi: spi-fsl-spi: automatically adapt bits-per-word in cpu mode Rasmus Villemoes
2019-04-01 7:34 ` [RFC PATCH 0/4] spi: spi-fsl-spi: try to make cpu-mode transfers faster Mark Brown
2019-04-02 8:43 ` Rasmus Villemoes
2019-04-02 9:10 ` Mark Brown [this message]
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=20190402091005.GC2059@sirena.org.uk \
--to=broonie@kernel.org \
--cc=Rasmus.Villemoes@prevas.se \
--cc=festevam@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-spi@vger.kernel.org \
--cc=rasmus.villemoes@prevas.dk \
/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).