On 4/20/20 5:50 PM, Andrew Lunn wrote: > On Mon, Apr 20, 2020 at 05:38:16PM +0200, Marek Vasut wrote: >> On 4/20/20 4:44 PM, Lukas Wunner wrote: >>> On Mon, Apr 20, 2020 at 04:24:05PM +0200, Marek Vasut wrote: >>>> On 4/20/20 4:20 PM, Lukas Wunner wrote: >>>>> On Mon, Apr 20, 2020 at 04:12:59PM +0200, Marek Vasut wrote: >>>>>> On 4/20/20 4:07 PM, Lukas Wunner wrote: >>>>>>> On Tue, Apr 14, 2020 at 08:20:17PM +0200, Marek Vasut wrote: >>>>>>>> The ks8851_rdreg32() is used only in one place, to read two registers >>>>>>>> using a single read. To make it easier to support 16-bit accesses via >>>>>>>> parallel bus later on, replace this single read with two 16-bit reads >>>>>>>> from each of the registers and drop the ks8851_rdreg32() altogether. >>>>>>>> >>>>>>>> If this has noticeable performance impact on the SPI variant of KS8851, >>>>>>>> then we should consider using regmap to abstract the SPI and parallel >>>>>>>> bus options and in case of SPI, permit regmap to merge register reads >>>>>>>> of neighboring registers into single, longer, read. >>>>>>> >>>>>>> Bisection has shown this patch to be the biggest cause of the >>>>>>> performance >>>>>>> regression introduced by this series: Latency increases by about 9 >>>>>>> usec. >>>>>> >>>>>> Just for completeness, did you perform this bisect on current linux-next >>>>>> without any patches except this series OR your patched rpi downstream >>>>>> vendor tree Linux 4.19 with preempt-rt patch applied ? >>>>> >>>>> The latter because latency without CONFIG_PREEMPT_RT_FULL=y is too >>>>> imprecise >>>>> to really see the difference and that's the configuration we care about. >>>> >>>> Why am I not able to see the same on the RPi3 then ? >>>> How can I replicate this observation ? >>> >>> Compile this branch with CONFIG_PREEMPT_RT_FULL=y: >>> >>> https://github.com/l1k/linux/commits/revpi-4.19-marek-v4 >>> >>> Alternatively, download this file: >>> >>> http://wunner.de/ks8851-marekv4.tar >>> >>> Install the "raspberrypi-kernel" deb-package included in the tarball on a >>> stock Raspbian image and copy one of the included ks8851.ko to: >>> /lib/modules/4.19.95-rt38-v7+/kernel/drivers/net/ethernet/micrel >> >> Why don't you rather try to replicate this problem in linux-next? > > Hi Lukas > > 4.19 is dead in terms of development work. It is now over 18 months > old. All mainline development work is done against either the last > -rc1 kernel, or a subsystems specific 'for-next' branch. > > Please test Marek patches against net-next. If there are performance > regressions with net-next, they should be addressed, but mainline does > not care about some random long time dead tree.
Are there any news on this one ?
