Re: [PATCH] RISC-V: Optimize bitops with Zbb extension

[Andrew Jones]

On Thu, Aug 31, 2023 at 09:37:30PM +0530, Anup Patel wrote:
> +Andrew
> 
> On Thu, Aug 31, 2023 at 9:29 PM Wang, Xiao W <xiao.w.wang@xxxxxxxxx> wrote:
> >
> >
> > > -----Original Message-----
> > > From: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> > > Sent: Wednesday, August 30, 2023 2:59 PM
> > > To: Wang, Xiao W <xiao.w.wang@xxxxxxxxx>
> > > Cc: Anup Patel <anup@xxxxxxxxxxxxxx>; paul.walmsley@xxxxxxxxxx;
> > > palmer@xxxxxxxxxxx; aou@xxxxxxxxxxxxxxxxx; ardb@xxxxxxxxxx; Li, Haicheng
> > > <haicheng.li@xxxxxxxxx>; linux-riscv@xxxxxxxxxxxxxxxxxxx; linux-
> > > efi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > > Subject: Re: [PATCH] RISC-V: Optimize bitops with Zbb extension
> > >
> > > On Wed, Aug 30, 2023 at 06:14:12AM +0000, Wang, Xiao W wrote:
> > > > Hi,
> > > >
> > > > > -----Original Message-----
> > > > > From: Anup Patel <anup@xxxxxxxxxxxxxx>
> > > > > Sent: Tuesday, August 29, 2023 7:08 PM
> > > > > To: Wang, Xiao W <xiao.w.wang@xxxxxxxxx>
> > > > > Cc: paul.walmsley@xxxxxxxxxx; palmer@xxxxxxxxxxx;
> > > > > aou@xxxxxxxxxxxxxxxxx; ardb@xxxxxxxxxx; Li, Haicheng
> > > > > <haicheng.li@xxxxxxxxx>; linux-riscv@xxxxxxxxxxxxxxxxxxx; linux-
> > > > > efi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > > > > Subject: Re: [PATCH] RISC-V: Optimize bitops with Zbb extension
> > > > >
> > > > > On Sun, Aug 6, 2023 at 8:09 AM Xiao Wang <xiao.w.wang@xxxxxxxxx>
> > > wrote:
> > > > > >
> > > > > > This patch leverages the alternative mechanism to dynamically optimize
> > > > > > bitops (including __ffs, __fls, ffs, fls) with Zbb instructions. When
> > > > > > Zbb ext is not supported by the runtime CPU, legacy implementation is
> > > > > > used. If Zbb is supported, then the optimized variants will be selected
> > > > > > via alternative patching.
> > > > > >
> > > > > > The legacy bitops support is taken from the generic C implementation as
> > > > > > fallback.
> > > > > >
> > > > > > If the parameter is a build-time constant, we leverage compiler builtin to
> > > > > > calculate the result directly, this approach is inspired by x86 bitops
> > > > > > implementation.
> > > > > >
> > > > > > EFI stub runs before the kernel, so alternative mechanism should not be
> > > > > > used there, this patch introduces a macro EFI_NO_ALTERNATIVE for this
> > > > > > purpose.
> > > > >
> > > > > I am getting the following compile error with this patch:
> > > > >
> > > > >   GEN     Makefile
> > > > >   UPD     include/config/kernel.release
> > > > >   UPD     include/generated/utsrelease.h
> > > > >   CC      kernel/bounds.s
> > > > > In file included from /home/anup/Work/riscv-
> > > > > test/linux/include/linux/bitmap.h:9,
> > > > >                  from
> > > > > /home/anup/Work/riscv-
> > > test/linux/arch/riscv/include/asm/cpufeature.h:9,
> > > > >                  from
> > > > > /home/anup/Work/riscv-test/linux/arch/riscv/include/asm/hwcap.h:90,
> > > >
> > > >
> > > > It looks there's a cyclic header including, which leads to this build error.
> > > > I checked https://github.com/kvm-riscv/linux/tree/master and
> > > > https://github.com/torvalds/linux/tree/master, but I don't see
> > > > "asm/cpufeature.h" is included in asm/hwcap.h:90, maybe I miss
> > > something,
> > > > could you help point me to the repo/branch I should work on?
> > >
> > > From MAINTAINERS:
> > >       RISC-V ARCHITECTURE
> > >       ...
> > >       T:      git git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git
> > >
> > > The for-next branch there is what you should be basing work on top of.
> > > AFAICT, you've made bitops.h include hwcap.h while cpufeature.h includes
> > > both bitops.h (indirectly) and hwcap.h.
> >
> > Thanks for the info, but I can't reproduce Anup's build error with this for-next branch, cpufeature.h is not included by hwcap.h there.
> > Maybe Anup could help double check the test environment?
> 
> I figured that cpufeature.h included in hwcap.h is added by
> Drew's patch "RISC-V: Enable cbo.zero in usermode"

I think we should probably split hwcap.h into two parts. The defines stay
and the rest can move to cpufeature.h

Thanks,
drew

> 
> I had tried this patch on-top-of dev-upstream branch of
> https://github.com/ventanamicro/linux.git
> 
> Regards,
> Anup
> 
> >
> > BRs,
> > Xiao
> >
> >
> > >
> > > Hope that helps,
> > > Conor.
> > >
> > > > >                  from
> > > > > /home/anup/Work/riscv-test/linux/arch/riscv/include/asm/bitops.h:26,
> > > > >                  from
> > > > > /home/anup/Work/riscv-test/linux/include/linux/bitops.h:68,
> > > > >                  from /home/anup/Work/riscv-test/linux/include/linux/log2.h:12,
> > > > >                  from /home/anup/Work/riscv-test/linux/kernel/bounds.c:13:
> > > > > /home/anup/Work/riscv-test/linux/include/linux/find.h: In function
> > > > > 'find_next_bit':
> > > > > /home/anup/Work/riscv-test/linux/include/linux/find.h:64:30: error:
> > > > > implicit declaration of function '__ffs'
> > > > > [-Werror=implicit-function-declaration]
> > > > >    64 |                 return val ? __ffs(val) : size;
> > > > >
> > > > > Regards,
> > > > > Anup
> > > > >
> > > > >
> > > > > >
> > > > > > Signed-off-by: Xiao Wang <xiao.w.wang@xxxxxxxxx>
> > > > > > ---
> > > > > >  arch/riscv/include/asm/bitops.h       | 266
> > > +++++++++++++++++++++++++-
> > > > > >  drivers/firmware/efi/libstub/Makefile |   2 +-
> > > > > >  2 files changed, 264 insertions(+), 4 deletions(-)
> > > > > >
> > > > > > diff --git a/arch/riscv/include/asm/bitops.h
> > > > > b/arch/riscv/include/asm/bitops.h
> > > > > > index 3540b690944b..f727f6489cd5 100644
> > > > > > --- a/arch/riscv/include/asm/bitops.h
> > > > > > +++ b/arch/riscv/include/asm/bitops.h
> > > > > > @@ -15,13 +15,273 @@
> > > > > >  #include <asm/barrier.h>
> > > > > >  #include <asm/bitsperlong.h>