On Wed, Dec 30, 2020 at 08:33:09PM +0100, Evgeni Golov wrote: > > And the tuned line that breaks the whole thing is > > > > [sysctl] > > kernel.sched_wakeup_granularity_ns = 15000000 > > This also happens on seabios 1.13.0-1 from snapshot.d.o. > > I originally wanted to go and bisect that with upstream seabios.git, but > then couldn't reproduce with upstreams 1.14.0… Until I realized that I > built it with CONFIG_ATA_DMA=y (as Debians 1.12) and indeed, this is > what was changed in 1.13 to n (see [1]) and also what does trigger the > bug you describe: with ATA_DMA=n the boot hangs, with ATA_DMA=y it boots > fine. > > Now understanding *why* ATA_DMA=n and sched_wakeup_granularity_ns > together have this result requires more scotch than I have at hand right > now. > > [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=934134
Just to write down some more facts… I can reproduce the issue by just poking /proc/sys/kernel/sched_wakeup_granularity_ns, so pretty sure it's not really tuned who is at foul here. The original value in my VM seems to be 1000000 and tuned raises that up to 15000000, which breaks things. I tried a bit around and the real breaking number seems to be somewhere between 2990000 and 3000000 (I didn't try to find the exact one yet). At least on my setup, no idea if that fluctuates between systems.
