Messages in this thread | | | Date | Sun, 22 May 2022 22:56:25 +0800 | From | Jisheng Zhang <> | Subject | Re: [PATCH 1/2] riscv: introduce unified static key mechanism for ISA extensions |
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On Sun, May 22, 2022 at 12:33:12AM -0700, Atish Patra wrote: > On Tue, May 17, 2022 at 11:53 AM Jisheng Zhang <jszhang@kernel.org> wrote: > > > > Currently, riscv has several extensions which may not be supported on > > all riscv platforms, for example, FPU and so on. To support unified > > kernel Image style, we need to check whether the feature is supported > > /s/suportted/supported
Thanks, will fix it in v2 soon. > > > or not. If the check sits at hot code path, then performance will be > > impacted a lot. static key can be used to solve the issue. In the past > > FPU support has been converted to use static key mechanism. I believe > > we will have similar cases in the future. > > > > this patch tries to add an unified mechanism to use static keys for > > some ISA extensions by implementing an array of default-false static keys > > and enabling them when detected. > > > > Signed-off-by: Jisheng Zhang <jszhang@kernel.org> > > --- > > arch/riscv/include/asm/hwcap.h | 40 ++++++++++++++++++++++++++++++++++ > > arch/riscv/kernel/cpufeature.c | 7 ++++++ > > 2 files changed, 47 insertions(+) > > > > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h > > index 0734e42f74f2..b0433d2b880d 100644 > > --- a/arch/riscv/include/asm/hwcap.h > > +++ b/arch/riscv/include/asm/hwcap.h > > @@ -12,6 +12,7 @@ > > #include <uapi/asm/hwcap.h> > > > > #ifndef __ASSEMBLY__ > > +#include <linux/jump_label.h> > > /* > > * This yields a mask that user programs can use to figure out what > > * instruction set this cpu supports. > > @@ -55,6 +56,16 @@ enum riscv_isa_ext_id { > > RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX, > > }; > > > > +/* > > + * This enum represents the logical ID for each RISC-V ISA extension static > > + * keys. We can use static key to optimize code path if some ISA extensions > > + * are available. > > + */ > > +enum riscv_isa_ext_key { > > + RISCV_ISA_EXT_KEY_FPU, /* For 'F' and 'D' */ > > + RISCV_ISA_EXT_KEY_MAX, > > +}; > > + > > struct riscv_isa_ext_data { > > /* Name of the extension displayed to userspace via /proc/cpuinfo */ > > char uprop[RISCV_ISA_EXT_NAME_LEN_MAX]; > > @@ -62,6 +73,35 @@ struct riscv_isa_ext_data { > > unsigned int isa_ext_id; > > }; > > > > +extern struct static_key_false riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_MAX]; > > + > > +static __always_inline int riscv_isa_ext2key(int num) > > +{ > > + switch (num) { > > + case RISCV_ISA_EXT_f: > > + return RISCV_ISA_EXT_KEY_FPU; > > + case RISCV_ISA_EXT_d: > > + return RISCV_ISA_EXT_KEY_FPU; > > + default: > > + return -EINVAL; > > + } > > +} > > + > > +/* > > + * @num must be a compile-time constant. > > + */ > > +static __always_inline bool riscv_isa_have_key_extension(int num) > > +{ > > + if (RISCV_ISA_EXT_ID_MAX <= num) > > + return false; > > + > > + num = riscv_isa_ext2key(num); > > + if (RISCV_ISA_EXT_KEY_MAX <= num || num < 0) > > + return false; > > + > > Why do you need the additional check in the hot path ? > riscv_isa_ext_keys array can be directly accessed at the caller > instead of calling this function.
directly accessing the keys can make the code simpler, thanks for the hint.
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