Messages in this thread | | | Date | Wed, 16 Nov 2016 18:01:56 +0000 | From | Brian Starkey <> | Subject | Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let ksoftirqd do its job" |
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Hi Eric,
On Wed, Nov 16, 2016 at 07:52:42AM -0800, Eric Dumazet wrote: >On Wed, Nov 16, 2016 at 5:55 AM, Brian Starkey <brian.starkey@arm.com> wrote: >> Hi, >> >> I'm running an ARM FVP (virtual platform - simluated hardware), which >> is failing to reach a login prompt due to extremely slow progress >> during boot. systemd gives up waiting for the ttyAMA0 device to >> appear, and never starts the getty. >> >> I've bisected this to commit 4cd13c21b207 "softirq: Let ksoftirqd do >> its job". >> >> Without this commit, the system boots to a login prompt in 2 minutes. >> With this commit, the system eventually manages to bring up sshd after >> 22 minutes, but as mentioned, the dev-ttyAMA0.device unit has timed >> out and so I don't get a prompt on my console. >> >> I only hit the issue when my rootfs is mounted over NFS, and with only >> a single core enabled. The (simulated) network device is an SMC91C111. >> With multiple cores enabled or a non-NFS filesystem, everything seems >> to work OK. >> >> I don't have an identical real hardware platform to try, but I >> could not reproduce it on a real ARM Juno board, which is similar. >> >> It looks from the logs that udev's workers are unable to make >> progress, so the device nodes don't get created. Don't pay too much >> attention to the timestamps in the logs below, they are "inside" the >> virtual platform, and don't reflect wall-clock time. >> Log before 4cd13c21b207: >> https://drive.google.com/open?id=0B8siaK6ZjvEwMktoa0NUS2hJd1U >> Log after 4cd13c21b207: >> https://drive.google.com/open?id=0B8siaK6ZjvEwZXlfeFFSQl9xZTQ >> Kernel config: arch/arm64/configs/defconfig >> >> I'm not sure how to debug this further, so if you have any suggestions >> I'd be glad to hear them. >> >> Many thanks, >> Brian >> > >Hi Brian. > >Thanks a lot for this report. > >If issue triggers when/if using one core, it is possible one driver >has a dependency on >softirqs being serviced during an initialization loop. > >If the thread is not yielding cpu (holding something like a spinlock >thus disabling preemption), >then ksoftirqd might not be able to run on the (same) cpu. >
The smc91x driver does seem to have some trickiness around softirqs. I'm not familiar with net drivers, but I'll see if I can figure anything out there.
>I sent a patch for busy polling yesterday, but I am almost certain >this would not fix your issue >(assuming you have CONFIG_PREEMPT) > >https://patchwork.ozlabs.org/patch/695185/
You're right in saying that this didn't help.
Thanks, Brian
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