Re: [RFC PATCH v2 00/29] PowerPC interrupt rework

[Cédric Le Goater]

Hello Matheus,

On 9/27/22 22:15, Matheus Ferst wrote:
> Link to v1: https://lists.gnu.org/archive/html/qemu-ppc/2022-08/msg00370.html
> This series is also available as a git branch: 
> https://github.com/PPC64/qemu/tree/ferst-interrupt-fix-v2

This is impressive work on QEMU PPC.

> This version addresses Fabiano's feedback and fixes some issues found
> with the tests suggested by Cédric. While working on it, I found two
> intermittent problems on master:
>
>   i) ~10% of boots with pSeries and 970/970mp/POWER5+ hard lockup after

These CPUs never got real attention with KVM. The FW was even broken
before 7.0.

>      either SCSI or network initialization when using -smp 4. With
>      -smp 2, the problem is harder to reproduce but still happens, and I
>      couldn't reproduce with thread=single.
> ii) ~52% of KVM guest initializations on PowerNV hang in different parts
>      of the boot process when using more than one CPU.

Do you mean when the guest is SMP or the host ?

> With the complete series applied, I couldn't reproduce (i) anymore, 

Super ! Models are getting better. This is nice for the 970.

> and (ii) became a little more frequent (~58%).

Have you checked 'info pic' ? XIVE is in charge of vCPU scheduling.
Could you please check with powersave=off in the host kernel also ?

> I've tested each patch of this series with [1], modified to use -smp for
> machines that support more than one CPU. The machines I can currently
> boot with FreeBSD (970/970,p/POWER5+/POWER7/POWER8/POWER9 pSeries,
> POWER8/POWER9 PowerNV, and mpc8544ds) were tested with the images from
> [2] and still boot after applying the patch series. Booting nested
> guests inside a TCG pSeries machine also seems to be working fine.
>
> Using command lines like:
>
> ./qemu-system-ppc64 -M powernv9 -cpu POWER9 -accel tcg,thread=multi \
>                  -m 8G -smp $SMP -vga none -nographic -kernel zImage \
>                  -append 'console=hvc0' -initrdootfs.cpio.xz \
>                  -serial pipe:pipe -monitor unix:mon,server,nowait
>
> and
>
> ./qemu-system-ppc64 -M pseries -cpu POWER9 -accel tcg,thread=multi \
>                  -m 8G -smp $SMP -vga none -nographic -kernel zImage \
>                  -append 'console=hvc0' -initrd rootfs.cpio.xz \
>                  -serial pipe:pipe -monitor unix:mon,server,nowait
>
> to measure the time to boot, login, and shut down a compressed kernel
> with a buildroot initramfs, with 100 iteration we get:
>
> +-----+------------------------------+-----------------------------+
> |     |            PowerNV           |           pSeries           |
> |-smp |------------------------------+-----------------------------+
> |     |     master    | patch series |    master    | patch series |
> +-----+------------------------------+-----------------------------+
> |  1  |  45,84 ± 0,92 | 38,08 ± 0,66 | 23,56 ± 1,16 | 23,76 ± 1,04 |
> |  2  |  80,21 ± 8,03 | 40,81 ± 0,45 | 26,59 ± 0,92 | 26,88 ± 0,99 |
> |  4  | 115,98 ± 9,85 | 38,80 ± 0,44 | 28,83 ± 0,84 | 28,46 ± 0,94 |
> |  6  | 199,14 ± 6,36 | 39,32 ± 0,50 | 29,22 ± 0,78 | 29,45 ± 0,86 |
> |  8  | 47,85 ± 27,50 | 38,98 ± 0,49 | 29,63 ± 0,80 | 29,60 ± 0,78 |
> +-----+------------------------------+-----------------------------+
>
> This results shows that the problem reported in [3] is solved, while

Yes. Nice work ! The PowerNV results with -smp 8 on master are unexpected.
Did you do some profiling also ?
 
> pSeries boot time is essentially unchanged.
>
>
> With a non-compressed kernel, the difference with PowerNV is smaller,
> and pSeries stills the same:
>
> +-----+------------------------------+-----------------------------+
> |     |            PowerNV           |           pSeries           |
> |-smp |------------------------------+-----------------------------+
> |     |     master    | patch series |    master    | patch series |
> +-----+------------------------------+-----------------------------+
> |  1  |  42,17 ± 0,92 | 38,13 ± 0,59 | 23,15 ± 1,02 | 23,46 ± 1,02 |
> |  2  |  55,72 ± 3,54 | 40,30 ± 0,56 | 26,26 ± 0,82 | 26,38 ± 0,80 |
> |  4  |  67,09 ± 3,02 | 38,26 ± 0,47 | 28,36 ± 0,77 | 28,19 ± 0,78 |
> |  6  |  98,96 ± 2,49 | 39,01 ± 0,38 | 28,68 ± 0,75 | 29,02 ± 0,88 |
> |  8  |  39,68 ± 0,42 | 38,44 ± 0,41 | 29,24 ± 0,81 | 29,44 ± 0,75 |
> +-----+------------------------------+-----------------------------+
>
> Finally, using command lines like
>
> ./qemu-system-ppc64 -M powernv9 -cpu POWER9 -accel tcg,thread=multi \
>      -m 8G -smp 4 -device virtio-scsi-pci -boot c -vga none -nographic \
>      -device nvme,bus=pcie.2,addr=0x0,drive=drive0,serial=1234 \
>      -drive file=rootfs.ext2,if=none,id=drive0,format=raw,cache=none \
>      -snapshot -serial pipe:pipe -monitor unix:mon,server,nowait \
>      -kernel zImage -append 'console=hvc0 rootwait root=/dev/nvme0n1' \
>      -device virtio-net-pci,netdev=br0,mac=52:54:00:12:34:57,bus=pcie.0 \
>      -netdev bridge,id=br0
>
> and
>
> ./qemu-system-ppc64 -M pseries -cpu POWER9 -accel tcg,thread=multi \
>      -m 8G -smp 4 -device virtio-scsi-pci -boot c -vga none -nographic \
>      -drive file=rootfs.ext2,if=scsi,index=0,format=raw -snapshot \
>      -kernel zImage -append 'console=hvc0 rootwait root=/dev/sda' \
>      -serial pipe:pipe -monitor unix:mon,server,nowait \
>      -device virtio-net-pci,netdev=br0,mac=52:54:00:12:34:57 \
>      -netdev bridge,id=br0
>
> to tests IO performance, with iperf to test network and a 4Gb scp
> transfer to test disk+network, in 100 iterations we saw:
>
> +---------------------+---------------+-----------------+
> |                     |    scp (s)    |   iperf (MB/s)  |
> +---------------------+---------------+-----------------+
> |PowerNV master       | 166,91 ± 8,37 | 918,06 ± 114,78 |
> |PowerNV patch series | 166,25 ± 8,85 | 916,91 ± 107,56 |
> |pSeries master       | 175,70 ± 8,22 | 958,73 ± 115,09 |
> |pSeries patch series | 173,62 ± 8,13 | 893,42 ±  87,77 |
> +---------------------+---------------+-----------------+

These are SMP machines under high IO load using MTTCG. It means
that the models are quite robust now.

> The scp data shows little difference, while testing just network shows
> that it's a bit slower with the patch series applied (although, with
> this variation, we'd probably need to repeat this test more times to
> have a more robust result...)

You could try with powersave=off.

Thanks,

C.



> [1] https://github.com/legoater/qemu-ppc-boot
> [2] https://artifact.ci.freebsd.org/snapshot/14.0-CURRENT/latest_vm/powerpc
> [3] https://lists.gnu.org/archive/html/qemu-ppc/2022-06/msg00336.html
>
> Matheus Ferst (29):
>    target/ppc: define PPC_INTERRUPT_* values directly
>    target/ppc: always use ppc_set_irq to set env->pending_interrupts
>    target/ppc: split interrupt masking and delivery from ppc_hw_interrupt
>    target/ppc: prepare to split interrupt masking and delivery by excp_model
>    target/ppc: create an interrupt masking method for POWER9/POWER10
>    target/ppc: remove unused interrupts from p9_pending_interrupt
>    target/ppc: create an interrupt deliver method for POWER9/POWER10
>    target/ppc: remove unused interrupts from p9_deliver_interrupt
>    target/ppc: remove generic architecture checks from p9_deliver_interrupt
>    target/ppc: move power-saving interrupt masking out of cpu_has_work_POWER9
>    target/ppc: add power-saving interrupt masking logic to 
> p9_next_unmasked_interrupt
>    target/ppc: create an interrupt masking method for POWER8
>    target/ppc: remove unused interrupts from p8_pending_interrupt
>    target/ppc: create an interrupt deliver method for POWER8
>    target/ppc: remove unused interrupts from p8_deliver_interrupt
>    target/ppc: remove generic architecture checks from p8_deliver_interrupt
>    target/ppc: move power-saving interrupt masking out of cpu_has_work_POWER8
>    target/ppc: add power-saving interrupt masking logic to 
> p8_next_unmasked_interrupt
>    target/ppc: create an interrupt masking method for POWER7
>    target/ppc: remove unused interrupts from p7_pending_interrupt
>    target/ppc: create an interrupt deliver method for POWER7
>    target/ppc: remove unused interrupts from p7_deliver_interrupt
>    target/ppc: remove generic architecture checks from p7_deliver_interrupt
>    target/ppc: move power-saving interrupt masking out of cpu_has_work_POWER7
>    target/ppc: add power-saving interrupt masking logic to 
> p7_next_unmasked_interrupt
>    target/ppc: remove ppc_store_lpcr from CONFIG_USER_ONLY builds
>    target/ppc: introduce ppc_maybe_interrupt
>    target/ppc: unify cpu->has_work based on cs->interrupt_request
>    target/ppc: move the p*_interrupt_powersave methods to excp_helper.c
>
>   hw/ppc/pnv_core.c        |   1 +
>   hw/ppc/ppc.c             |  17 +-
>   hw/ppc/spapr_hcall.c     |   6 +
>   hw/ppc/spapr_rtas.c      |   2 +-
>   hw/ppc/trace-events      |   2 +-
>   target/ppc/cpu.c         |   4 +
>   target/ppc/cpu.h         |  43 +-
>   target/ppc/cpu_init.c    | 212 +---------
>   target/ppc/excp_helper.c | 857 ++++++++++++++++++++++++++++++++++-----
>   target/ppc/helper.h      |   1 +
>   target/ppc/helper_regs.c |   2 +
>   target/ppc/misc_helper.c |  11 +-
>   target/ppc/translate.c   |   2 +
>   13 files changed, 803 insertions(+), 357 deletions(-)