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

[Wang, Xiao W]

> -----Original Message-----
> From: Conor Dooley <conor.dooley at microchip.com>
> Sent: Wednesday, August 30, 2023 2:59 PM
> To: Wang, Xiao W <xiao.w.wang at intel.com>
> Cc: Anup Patel <anup at brainfault.org>; paul.walmsley at sifive.com;
> palmer at dabbelt.com; aou at eecs.berkeley.edu; ardb at kernel.org; Li, Haicheng
> <haicheng.li at intel.com>; linux-riscv at lists.infradead.org; linux-
> efi at vger.kernel.org; linux-kernel at vger.kernel.org
> 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 at brainfault.org>
> > > Sent: Tuesday, August 29, 2023 7:08 PM
> > > To: Wang, Xiao W <xiao.w.wang at intel.com>
> > > Cc: paul.walmsley at sifive.com; palmer at dabbelt.com;
> > > aou at eecs.berkeley.edu; ardb at kernel.org; Li, Haicheng
> > > <haicheng.li at intel.com>; linux-riscv at lists.infradead.org; linux-
> > > efi at vger.kernel.org; linux-kernel at vger.kernel.org
> > > Subject: Re: [PATCH] RISC-V: Optimize bitops with Zbb extension
> > >
> > > On Sun, Aug 6, 2023 at 8:09 AM Xiao Wang <xiao.w.wang at intel.com>
> 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?

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 at intel.com>
> > > > ---
> > > >  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>