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Subject: Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support
To:     Mark Brown <broonie@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>
Cc:     Florian Fainelli <f.fainelli@gmail.com>, lukas@wunner.de,
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        Rob Herring <robh+dt@kernel.org>,
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        Martin Sperl <kernel@martin.sperl.org>,
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From:   Florian Fainelli <f.fainelli@gmail.com>
Message-ID: <bb9dbf11-9e33-df60-f5ae-f7fdfe8458b4@gmail.com>
Date:   Mon, 15 Jun 2020 09:34:58 -0700
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On 6/8/2020 4:28 AM, Mark Brown wrote:
> On Mon, Jun 08, 2020 at 12:11:11PM +0100, Robin Murphy wrote:
> 
>> Again, 2 cycles. The overhead of a static key alone is at least 50% of that.
>> And that's not even considering whether the change in code layout caused by
>> doubling up the IRQ handler might affect I-cache or branch predictor
>> behaviour, where a single miss stands to more than wipe out any perceived
>> saving. And all in code that has at least one obvious inefficiency left on
>> the table either way.
> 
>> This thread truly epitomises Knuth's "premature optimisation" quote... ;)
> 
> In fairness the main reason this driver is so heavily tuned already (and
> has lead to some really nice improvements in the core) is that there are
> a number of users hitting 100% CPU utilization driving SPI devices on
> some of the older RPi hardware, IIRC around IIO type applications
> mostly.  I do tend to agree that this particular optimization is a bit
> marginal but there has been a lot of effort put into this.

OK, so this has been dropped for spi/for-next right? How do we move from
there?
-- 
Florian