Hi Pedro,
The GIC is indeed the likely culprit as 8 PEs is the architectural limit of
GICv2 (which is the interrupt controller used by VExpress_GEM5_V1, the default
fs_bigLITTLE.py platform).
If using KVM I honestly don’t see an easy way around it: we have on upstream a
device driver modification which allows to instantiate more than 8 CPUs with
GICv2 [1]. It works if used in fully simulated CPU models; I suspect this won’t
work with KVM though.
We have recently provided support for KVM simulations with GICv3 [2]. This has
been merged on develop and it will be part of the next gem5 release. This will
allow FS simulations with more than 8 KVM CPUs. So either you base your work on
develop, or you try to backport those patches to 21.1.0.2
Kind Regards
Giacomo
[1]:
https://gem5.googlesource.com/arm/linux/+/a2e8bda41866718ade4856d31f6c87e7234a3add
[2]: https://gem5-review.googlesource.com/c/public/gem5/+/55615
From: Pedro Becker via gem5-users
Date: Wednesday, 16 March 2022 at 15:35
To: gem5-users@gem5.org
Cc: Pedro Becker
Subject: [gem5-users] Boot gets stuck sometimes ARM FS + KVM + 8 CPUs
Hi all
I'm trying to boot arm FS with KVM in an ARM machine (an Nvidia Jetson) with
multiple cores.
I had it working last year, on gem5 version 21.1.0.0. Later I had to update
gem5 to version 21.1.0.2 because of some
errors in the stats generation of version 21.1.0.0.
So I had a lot of problems in the way, which were discussed here
(https://lists.gem5.org/archives/list/gem5-users@gem5.org/thread/VCI74JOSRCQK3N64QRRGV3HLNVEYH4OC/#VCI74JOSRCQK3N64QRRGV3HLNVEYH4OC).
But it was working.
Now I'm back on using that setup, but I'm getting a weird behavior using the
fs_bigLITTLE.py script:
Basically, the boot is inconsistent with 8 CPUs. Sometimes it boots, sometimes
it gets stuck at
[0.194001] smp: Bringing up secondary CPUs ...
I'm varying the numbers of and (such that
+ <= 8) in the command below:
./build/ARM/gem5.opt configs/example/arm/fs_bigLITTLE.py --kernel
/scratch/pedro/aarch-my-system/binaries/vmlinux.arm64 --disk
/scratch/pedro/ubuntu-18.04-arm64-8gb.img --cpu-type kvm --kvm-userspace-gic
--mem-size 8GB --big-cpus --little-cpus --bootscript
configs/boot/hello.rcS
Using 8 big CPUs generally cause it to get stuck, actually. Using 7 or fewer
CPUs never made caused it to get stuck. Big little configurations seem to boot
fine (e.g. 6 big + 2 little).
I wonder if it is because of using a simulated GIC to provide support to 8 CPUs.
Is that a known behavior?
Any workaround?
Thank you.
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