Re: [PATCH v6 1/1] eal/riscv: optimize rte_memcpy with vector and zicbop extensions

[sunyuechi <sunyuechi@iscas.ac.cn>]

 > > # detect extensions
 > > # Requires intrinsics available in GCC 14.1.0+ and Clang 18.1.0+
 > > if (riscv_extension_macros and
 > >     (cc.get_define('__riscv_zicbop', args: machine_args) != ''))
 > >   if ((cc.get_id() == 'gcc' and 
cc.version().version_compare('>=14.1.0'))
 > >       or (cc.get_id() == 'clang' and 
cc.version().version_compare('>=18.1.0')))
 > >       message('Compiling with the zicbop extension')
 > >       machine_args += ['-DRTE_RISCV_FEATURE_PREFETCH']
 > >   else
 > >     warning('Detected zicbop extension but cannot use because 
intrinsics are not available (present in GCC 14.1.0+ and Clang 18.1.0+)')
 > >   endif
 > > endif
 >
 > The implementation does not involve intrinsics

It looks like nothing has been changed here yet.

 > #if defined(RTE_RISCV_FEATURE_V) && 
!(defined(RTE_RISCV_FEATURE_PREFETCH))
 > #undef RTE_RISCV_FEATURE_V
 > #endif
 >
 > static __rte_always_inline void
 > _rte_mov128blocks(uint8_t *dst, const uint8_t *src, size_t n)
 > {
 >     asm volatile (
 >         "prefetch.r 64(%1)\n"
 >         "prefetch.w 64(%0)\n"
 >         "prefetch.r 128(%1)\n"
 >         "prefetch.w 128(%0)\n"
 >         "prefetch.r 192(%1)\n"
 >         "prefetch.w 192(%0)\n"
 >         "prefetch.r 256(%1)\n"
 >         "prefetch.w 256(%0)\n"
 >         "prefetch.r 320(%1)\n"
 >         "prefetch.w 320(%0)\n"
 >         "prefetch.r 384(%1)\n"
 >         "prefetch.w 384(%0)\n"
 >         "prefetch.r 448(%1)\n"
 >         "prefetch.w 448(%0)\n"
 >         "prefetch.r 512(%1)\n"
 >         "li t6, 512\n"
 >         "3:\n"
 >         "li t5, 128;"
 >         "vsetvli zero, t5, e8, m8, ta, ma\n"

With the current compilation conditions, if zicbop isn’t supported, the 
v-optimization also won’t be compiled.
Have you tested the performance difference if you remove these 
prefetches and only use v?
Can we use a condition like this to support only v?

#if defined(RTE_RISCV_FEATURE_V)
    #if (defined(RTE_RISCV_FEATURE_PREFETCH))
         ...
    #endif
     ...
#endif