On 2024/6/6 上午11:42, Richard Henderson wrote:
On 6/5/24 20:36, maobibo wrote:
static biz_accel_fn const accel_table[] = {
buffer_is_zero_int_ge256,
#ifdef __loongarch_sx
buffer_is_zero_lsx,
#endif
#ifdef __loongarch_asx
buffer_is_zero_lasx,
#endif
};
static unsigned best_accel(void)
{
#ifdef __loongarch_asx
/* lasx may be index 1 or 2, but always last */
return ARRAY_SIZE(accel_table) - 1;
#else
/* lsx is always index 1 */
return 1;
#endif
}
size of accel_table is decided at compile-time, will it be better if
runtime checking is added also? something like this:
unsigned info = cpuinfo_init();
#ifdef __loongarch_asx
if (info & CPUINFO_LASX) {
/* lasx may be index 1 or 2, but always last */
return ARRAY_SIZE(accel_table) - 1;
}
#endif
No, because the ifdef checks that the *compiler* is prepared to use
LASX/LSX instructions itself without further checks. There's no point
in qemu checking further.
By my understanding, currently compiler option is the same with all
files, there is no separate compiler option with single file or file
function.
So if compiler is prepared to use LASX/LSX instructions itself, host
hardware must support LASX/LSX instructions, else there will be problem.
My main concern is that there is one hw machine which supports LSX, but
no LASX, no KVM neither. QEMU binary maybe fails to run on such hw
machine if it is compiled with LASX option.
Regards
Bibo Mao
r~
