[PATCH] riscv, bpf: Optimize zextw insn with Zba extension

[Wang, Xiao W]

> -----Original Message-----
> From: Conor Dooley <conor at kernel.org>
> Sent: Saturday, May 11, 2024 4:56 AM
> 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; luke.r.nels at gmail.com; xi.wang at gmail.com;
> bjorn at kernel.org; ast at kernel.org; daniel at iogearbox.net; andrii at kernel.org;
> martin.lau at linux.dev; eddyz87 at gmail.com; song at kernel.org;
> yonghong.song at linux.dev; john.fastabend at gmail.com; kpsingh at kernel.org;
> sdf at google.com; haoluo at google.com; jolsa at kernel.org; linux-
> riscv at lists.infradead.org; linux-kernel at vger.kernel.org; bpf at vger.kernel.org;
> pulehui at huawei.com; Li, Haicheng <haicheng.li at intel.com>
> Subject: Re: [PATCH] riscv, bpf: Optimize zextw insn with Zba extension
> 
> On Tue, May 07, 2024 at 06:45:28PM +0800, Xiao Wang wrote:
> > The Zba extension provides add.uw insn which can be used to implement
> > zext.w with rs2 set as ZERO.
> >
> > Signed-off-by: Xiao Wang <xiao.w.wang at intel.com>
> > ---
> >  arch/riscv/Kconfig       | 19 +++++++++++++++++++
> >  arch/riscv/net/bpf_jit.h | 18 ++++++++++++++++++
> >  2 files changed, 37 insertions(+)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 6bec1bce6586..0679127cc0ea 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -586,6 +586,14 @@ config RISCV_ISA_V_PREEMPTIVE
> >  	  preemption. Enabling this config will result in higher memory
> >  	  consumption due to the allocation of per-task's kernel Vector
> context.
> >
> > +config TOOLCHAIN_HAS_ZBA
> > +	bool
> > +	default y
> > +	depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zba)
> > +	depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zba)
> > +	depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
> > +	depends on AS_HAS_OPTION_ARCH
> > +
> >  config TOOLCHAIN_HAS_ZBB
> >  	bool
> >  	default y
> > @@ -601,6 +609,17 @@ config TOOLCHAIN_HAS_VECTOR_CRYPTO
> >  	def_bool $(as-instr, .option arch$(comma) +v$(comma) +zvkb)
> >  	depends on AS_HAS_OPTION_ARCH
> >
> > +config RISCV_ISA_ZBA
> > +	bool "Zba extension support for bit manipulation instructions"
> > +	depends on TOOLCHAIN_HAS_ZBA
> > +	depends on RISCV_ALTERNATIVE
> > +	default y
> > +	help
> > +	   Adds support to dynamically detect the presence of the ZBA
> > +	   extension (address generation acceleration) and enable its usage.
> 
> Recently I sent some patches to reword other extensions' help text,
> because the "add support to dynamically detect" had confused people a
> bit. Dynamic detection is done regardless of config options for Zba.
> The wording I went with in my patch for Zbb was:
> 	   Add support for enabling optimisations in the kernel when the
> 	   Zbb extension is detected at boot.
> Could you use something similar here in the opening sentence please?

Agree with you. Yes, I would reword it in next version.

Thanks,
Xiao

> 
> Thanks,
> Conor.