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Hi all, Although Florian was concerned about a trivial inline check to deal with shared IRQs adding overhead, the reality is that it would be so small as to not be worth even thinking about unless the driver was already tuned to squeeze out every last cycle. And a brief look over the code shows that that clearly isn't the case. This is an example of some of the easy low-hanging fruit that jumps out just from code inspection. Based on disassembly and ARM1176 cycle timings, patch #2 should save the equivalent of 2-3 shared interrupt checks off the critical path in all cases, and patch #3 possibly up to about 100x more. I don't have any means to test these patches, let alone measure performance, so they're only backed by the principle that less code - and in particular fewer memory accesses - is almost always better. There is almost certainly a *lot* more to be had from careful use of relaxed I/O accessors, not doing a read-modify-write of CS at every reset, tweaking the loops further to avoid unnecessary writebacks to variables, and so on. However since I'm not invested in this personally I'm not going to pursue it any further; I'm throwing these patches out as more of a demonstration to back up my original drive-by review comments, so if anyone want to pick them up and run with them then please do so. Robin. Robin Murphy (3): spi: bcm3835: Tidy up bcm2835_spi_reset_hw() spi: bcm2835: Micro-optimise IRQ handler spi: bcm2835: Micro-optimise FIFO loops drivers/spi/spi-bcm2835.c | 45 +++++++++++++++++++-------------------- 1 file changed, 22 insertions(+), 23 deletions(-) -- 2.23.0.dirty _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.