Re: [PATCH v3 2/2] perf bench: Add support for 32-bit systems with 64-bit time_t

[André Almeida]

Hi Alistair,

Às 03:10 de 17/09/21, Alistair Francis escreveu:
> From: Alistair Francis <alistair.francis@xxxxxxx>
> 
> Some 32-bit architectures (such are 32-bit RISC-V) only have a 64-bit
> time_t and as such don't have the SYS_futex syscall. This patch will
> allow us to use the SYS_futex_time64 syscall on those platforms.
> 

Thanks for your patch! However, I don't think that any futex operation
at perf has timeout. Do you plan to implement a test that use it? Or the
idea is to get this ready for it in case someone want to do so in the
future?


Also, I faced a similar problem with the new futex2 syscalls, that
supports exclusively 64bit timespec. But I took a different approach: I
called __NR_clock_gettime64 for 32bit architectures so it wouldn't
require to convert the struct:

#if defined(__i386__) || __TIMESIZE == 32
# define NR_gettime64 __NR_clock_gettime64
#else
# define NR_gettime64 __NR_clock_gettime
#endif

struct timespec64 {
	long long tv_sec;	/* seconds */
	long long tv_nsec;	/* nanoseconds */
};

int gettime64(clock_t clockid, struct timespec64 *tv)
{
	return syscall(NR_gettime64, clockid, tv);
}

Then we can just use &timeout at __NR_futex_time64 for 32bit arch and at
__NR_futex for 64bit arch.

This might be a simpler solution to the problem that you are facing but
I'm not entirely sure. Also, futex's selftests do use the timeout
argument and I think that they also won't compile in 32-bit RISC-V, so
maybe we can start from there so we can actually test the timeout
argument and check if it's working.

Thanks,
	André