Hey Arnd/Guenter, On Wed, Mar 23, 2022 at 4:53 PM Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Wed, Mar 23, 2022 at 3:23 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote: > > > > On 3/23/22 05:10, Mark Brown wrote: > > > On Tue, Mar 22, 2022 at 02:54:20PM -0700, Guenter Roeck wrote: > > > Kind of academic given that Jason seems to have a handle on what the > > > issues are but for KernelCI it's variations on mach-virt, plus > > > versatile-pb. There's a physical cubietruck as well, and BeagleBone > > > Blacks among others. My best guess would be systems with low RAM are > > > somehow more prone to issues. > > > > I don't think it is entirely academic. versatile-pb fails for me; > > if it doesn't fail at KernelCI, I'd like to understand why - not to > > fix it in my test environment, but to make sure that I _don't_ fix it. > > After all, it _is_ a regression. Even if that regression is triggered > > by bad (for a given definition of "bad") userspace code, it is still > > a regression. > > Maybe kernelci has a virtio-rng device assigned to the machine > and you don't? That would clearly avoid the issue here. Indeed it's probably something like that. Or maybe they're networked with something that has a steady stream of interrupts. I say this because I was able to reproduce Guenter's findings using the versatilepb machine with the versatile_defconfig config and the versatile-pb.dtb file. Indeed this board doesn't have a cycle counter. However, I did have success using the fallback timer and the other patches in the jd/for-guenter branch, so at least for versatile's nuances, I think (hope?) there's a reasonable success story here. Jason
