From: Mark Brown <broonie@kernel.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE"
<linux-arm-kernel@lists.infradead.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
Florian Fainelli <f.fainelli@gmail.com>,
Scott Branden <sbranden@broadcom.com>,
lukas@wunner.de, Ray Jui <rjui@broadcom.com>,
linux-kernel@vger.kernel.org,
"open list:SPI SUBSYSTEM" <linux-spi@vger.kernel.org>,
Rob Herring <robh+dt@kernel.org>,
"maintainer:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..."
<bcm-kernel-feedback-list@broadcom.com>,
"moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE"
<linux-rpi-kernel@lists.infradead.org>,
Martin Sperl <kernel@martin.sperl.org>,
Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Subject: Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support
Date: Fri, 5 Jun 2020 16:27:39 +0100 [thread overview]
Message-ID: <20200605152739.GH5413@sirena.org.uk> (raw)
In-Reply-To: <06342e88-e130-ad7a-9f97-94f09156f868@arm.com>
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On Fri, Jun 05, 2020 at 03:41:27PM +0100, Robin Murphy wrote:
> Ha, and in fact having checked a build out of curiosity, this patch as-is
> actually stands to make things considerably worse. At least with GCC 8.3 and
> bcm2835_defconfig, bcm2835_spi_interrupt_common() doesn't get inlined, which
> means bcm2835_spi_interrupt() pushes/pops a stack frame and makes an
> out-of-line call to bcm2835_spi_interrupt_common(), resulting in massively
> *more* work than the extra two instructions of simply inlining the test.
Whichever compiler I was using (clang-11 probably) did manage to inline
the tail call so it really was the two instructions but yeah, in general
this approach is going to be fragile.
> So yes, the overhead of inlining the test vs. the alternative is indeed
> non-zero. It's just also negative :D
And variable!
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next prev parent reply other threads:[~2020-06-05 15:27 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-04 21:28 [PATCH v2] spi: bcm2835: Enable shared interrupt support Florian Fainelli
2020-06-05 8:46 ` Nicolas Saenz Julienne
2020-06-05 10:52 ` Mark Brown
2020-06-05 10:58 ` Nicolas Saenz Julienne
2020-06-05 10:51 ` Lukas Wunner
2020-06-05 11:14 ` Mark Brown
2020-06-05 12:20 ` Mark Brown
2020-06-05 11:34 ` Robin Murphy
2020-06-05 13:20 ` Mark Brown
2020-06-05 13:46 ` Robin Murphy
2020-06-05 14:41 ` Robin Murphy
2020-06-05 15:27 ` Mark Brown [this message]
2020-06-05 22:04 ` Florian Fainelli
2020-06-08 11:11 ` Robin Murphy
2020-06-08 11:28 ` Mark Brown
2020-06-15 16:34 ` Florian Fainelli
2020-06-15 17:00 ` Mark Brown
2020-06-15 17:04 ` Florian Fainelli
2020-06-15 17:30 ` Mark Brown
2020-06-15 17:31 ` Robin Murphy
2020-06-15 19:26 ` Mark Brown
2020-06-08 11:41 ` Lukas Wunner
2020-06-15 19:09 ` Robin Murphy
2020-06-15 19:42 ` Florian Fainelli
2020-06-15 20:48 ` Mark Brown
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