On 2018-12-06 15:31:50 [+0100], Luca Abeni wrote: > Update, after more tests: > - With all the "*DEBUG*" entries disabled in .config, "nohz=off" in > the kernel command line and the i915 driver disabled in .config, I > consistently get a worst-case latency below 40us (this is the order of > magnitude I was expecting). Good > - With everything as in the above configuration, but enabling the i915 > driver in .config, I get a worst case latency of about 80us. Applying > Sebastian's patch does not seem to affect the latency. I also disabled > the various tracing options in .config, but the maximum latency is > still around 80us. The patch should avoid the backtrace you sent at the begin of this thread. This one happens otherwise if you enable the i915 events. > The latencies mentioned above have been measured with > cyclictest -n -p 80 -i 50 -t 1 -m -a > while running "du -h /" and a "make -j 2" of the kernel in background. So this should fire one thread on CPU0 up and I believe and pin it there. That interval looks very low. I would suggest to increment it around 200 or so. > So, the numbers I get now are much better, but the i915 driver still > seems to create some real-time issues. The i915 could increase the latency a little. You could try to add i915.enable_dc=0 i915.enable_rc6=0 to disable power management on the GPU. > > Luca > Sebastian
