On 2022-11-28 12:53, Marc Zyngier wrote:
On Mon, 28 Nov 2022 17:08:31 +0000, Luiz Capitulino luizcap@amazon.com wrote:
Hi,
[ Marc, can you help reviewing? Esp. the first patch? ]
This series of backports from upstream to stable 5.15 and 5.10 fixes an issue we're seeing on AWS ARM instances where attaching an EBS volume (which is a nvme device) to the instance after offlining CPUs causes the device to take several minutes to show up and eventually nvme kworkers and other threads start getting stuck.
This series fixes the issue for 5.15.79 and 5.10.155. I can't reproduce it on 5.4. Also, I couldn't reproduce this on x86 even w/ affected kernels.
That's because x86 has a very different allocation policy compared to what the ITS does. The x86 vector space is tiny, so vectors are only allocated when required. In your case, that's when the CPUs are onlined.
With the ITS, all the vectors are allocated upfront, as this is essentially free. But in the case of managed interrupts, these vectors are now pointing to offline CPUs. The ITS tries to fix that, but doesn't nearly have enough information. And the correct course of action is to keep these interrupts in the shutdown state, which is what the series is doing.
Thank you for the explanation, Marc. I also immensely
appreciate the super fast response! (more below).
An easy reproducer is:
- Start an ARM instance with 32 CPUs
To satisfy my own curiosity, is that in a guest or bare metal? It shouldn't make any difference, but hey...
This is a guest. I'll test on a bare-metal instance, it may
take a few hours. I'll reply here.
Anyway, patch #1 looks OK to me, but I haven't tried to dig further into something that is "oh so last year" ;-). Specially as we're rewriting the whole of the MSI stack! FWIW:
Acked-by: Marc Zyngier maz@kernel.org
Thank you again, Marc!
M.-- Without deviation from the norm, progress is not possible.