Re: [PATCH V2] raid6: Add RISC-V SIMD syndrome and recovery calculations

[Charlie Jenkins <charlie@rivosinc.com>]

On Tue, Feb 11, 2025 at 05:59:26PM +0800, Chunyan Zhang wrote:
> On Tue, 28 Jan 2025 at 06:34, Charlie Jenkins <charlie@rivosinc.com> wrote:
> >
> > On Mon, Jan 27, 2025 at 09:39:11AM +0100, Paul Menzel wrote:
> > > Dear Chunyan,
> > >
> > >
> > > Thank you for the patch.
> > >
> > >
> > > Am 27.01.25 um 07:15 schrieb Chunyan Zhang:
> > > > The assembly is originally based on the ARM NEON and int.uc, but uses
> > > > RISC-V vector instructions to implement the RAID6 syndrome and
> > > > recovery calculations.
> > > >
> > > > Results on QEMU running with the option "-icount shift=0":
> > > >
> > > >    raid6: rvvx1    gen()  1008 MB/s
> > > >    raid6: rvvx2    gen()  1395 MB/s
> > > >    raid6: rvvx4    gen()  1584 MB/s
> > > >    raid6: rvvx8    gen()  1694 MB/s
> > > >    raid6: int64x8  gen()   113 MB/s
> > > >    raid6: int64x4  gen()   116 MB/s
> > > >    raid6: int64x2  gen()   272 MB/s
> > > >    raid6: int64x1  gen()   229 MB/s
> > > >    raid6: using algorithm rvvx8 gen() 1694 MB/s
> > > >    raid6: .... xor() 1000 MB/s, rmw enabled
> > > >    raid6: using rvv recovery algorithm
> > >
> > > How did you start QEMU and on what host did you run it? Does it change
> > > between runs? (For me these benchmark values were very unreliable in the
> > > past on x86 hardware.)
> >
> > I reported dramatic gains on vector as well in this response [1]. Note
> > that these gains are only present when using the QEMU option "-icount
> > shift=0" vector becomes dramatically more performant. Without this
> > option we do not see a performance gain on QEMU. However riscv vector is
> > known to not be less optimized on QEMU so having vector be less
> > performant on some QEMU configurations is not necessarily representative
> > of hardware implementations.
> >
> >
> > My full qemu command is (running on x86 host):
> >
> > qemu-system-riscv64 -nographic -m 1G -machine virt -smp 1\
> >     -kernel arch/riscv/boot/Image \
> >     -append "root=/dev/vda rw earlycon console=ttyS0" \
> >     -drive file=rootfs.ext2,format=raw,id=hd0,if=none \
> >     -bios default -cpu rv64,v=true,vlen=256,vext_spec=v1.0 \
> >     -device virtio-blk-device,drive=hd0
> >
> > This is with version 9.2.0.
> >
> >
> > I am also facing this issue when executing this:
> >
> > raid6: rvvx1    gen()   717 MB/s
> > raid6: rvvx2    gen()   734 MB/s
> > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
> >
> > Only rvvx4 is failing. I applied this patch to 6.13.
> 
> I used your command to run but no issue on my side (x86 host, qemu
> version is 9.2.0, kernel 6.13 too):
> 
> qemu-system-riscv64 -nographic -m 1G -machine virt -smp 1 -icount shift=0 \
>         -kernel arch/riscv/boot/Image   \
>         -append "rootwait root=/dev/vda ro"     \
>         -drive file=rootfs.ext4,format=raw,id=hd0 \
>         -bios default -cpu rv64,v=true,vlen=256,vext_spec=v1.0 \
>         -device virtio-blk-device,drive=hd0

I am able to reproduce it with this defconfig:

CONFIG_SYSVIPC=y
CONFIG_NO_HZ_IDLE=y
CONFIG_HIGH_RES_TIMERS=y
CONFIG_BPF_SYSCALL=y
CONFIG_IKCONFIG=y
CONFIG_IKCONFIG_PROC=y
CONFIG_NAMESPACES=y
CONFIG_USER_NS=y
CONFIG_CHECKPOINT_RESTORE=y
CONFIG_BLK_DEV_INITRD=y
CONFIG_EXPERT=y
# CONFIG_SYSFS_SYSCALL is not set
CONFIG_PROFILING=y
CONFIG_SMP=y
CONFIG_CPU_FREQ=y
CONFIG_CPU_FREQ_STAT=y
CONFIG_CPU_FREQ_GOV_USERSPACE=y
CONFIG_CPU_FREQ_GOV_ONDEMAND=y
CONFIG_CPUFREQ_DT=y
CONFIG_JUMP_LABEL=y
CONFIG_DEVTMPFS=y
CONFIG_DEVTMPFS_MOUNT=y
CONFIG_MTD=y
CONFIG_MTD_BLOCK=y
CONFIG_MTD_CFI=y
CONFIG_MTD_CFI_ADV_OPTIONS=y
CONFIG_BLK_DEV_LOOP=y
CONFIG_VIRTIO_BLK=y
CONFIG_MD=y
CONFIG_BLK_DEV_MD=y
CONFIG_MD_RAID456=y
CONFIG_INPUT_MOUSEDEV=y
CONFIG_SERIAL_8250=y
CONFIG_SERIAL_8250_CONSOLE=y
CONFIG_SERIAL_8250_DW=y
CONFIG_SERIAL_OF_PLATFORM=y
CONFIG_SERIAL_SIFIVE=y
CONFIG_SERIAL_SIFIVE_CONSOLE=y
CONFIG_VIRTIO_CONSOLE=y
CONFIG_HW_RANDOM_VIRTIO=y
CONFIG_PINCTRL=y
CONFIG_GPIOLIB=y
CONFIG_GPIO_DWAPB=y
CONFIG_GPIO_SIFIVE=y
CONFIG_SOUND=y
CONFIG_RTC_CLASS=y
CONFIG_RTC_DRV_GOLDFISH=y
CONFIG_DMADEVICES=y
CONFIG_DW_AXI_DMAC=y
CONFIG_VIRTIO_BALLOON=y
CONFIG_VIRTIO_INPUT=y
CONFIG_VIRTIO_MMIO=y
CONFIG_GOLDFISH=y
CONFIG_MAILBOX=y
CONFIG_RPMSG_CTRL=y
CONFIG_RPMSG_VIRTIO=y
CONFIG_PM_DEVFREQ=y
CONFIG_IIO=y
CONFIG_LIBNVDIMM=y
CONFIG_EXT4_FS=y
CONFIG_EXT4_FS_POSIX_ACL=y
CONFIG_EXT4_FS_SECURITY=y
CONFIG_AUTOFS_FS=y
CONFIG_ISO9660_FS=y
CONFIG_JOLIET=y
CONFIG_ZISOFS=y
CONFIG_MSDOS_FS=y
CONFIG_VFAT_FS=y
CONFIG_PRINTK_TIME=y
CONFIG_SCHED_STACK_END_CHECK=y
# CONFIG_RCU_TRACE is not set
# CONFIG_FTRACE is not set
# CONFIG_RUNTIME_TESTING_MENU is not set

I took the riscv/defconfig and added MD_RAID456 and it's dependencies.
So that the message wasn't too long I started removing some unnecessary
configs. Try this out and let me know if you encounter the issue.

- Charlie

> 
> Thanks,
> Chunyan
> 
> >
> > - Charlie
> >