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
