Re: [PATCH 0/3] MR6031: Draft: winewayland: Use fast atomic locks insted pthread_mutex.

[Alfred Agrell (＠Alcaro)]

Alfred Agrell (@Alcaro) commented about dlls/winewayland.drv/waylanddrv.h:
> +#include <stdint.h>
> +#include <unistd.h>
> +#include <linux/futex.h>
> +#include <sys/syscall.h>
> +#define WINEWAYLAND_USE_ATOMIC
> +#define WINEWAYLAND_RESOURCE_TYPE _Atomic unsigned char
> +#define WINEWAYLAND_RESOURCE_INIT ATOMIC_VAR_INIT(0)
> +#define WINEWAYLAND_RESOURCE_LOCK(RESOURCE) {                       \
> - unsigned char expected = 0;                                           \
> - while(!atomic_compare_exchange_weak(RESOURCE, &expected, 1)) {  \
> -
>    syscall(SYS_futex, RESOURCE, FUTEX_WAIT, 1, NULL, NULL, 0); \
> - }                                                               \
>
> +}
> +#define WINEWAYLAND_RESOURCE_UNLOCK(RESOURCE) {                 \
> - atomic_store(RESOURCE, 0);                                  \
> - syscall(SYS_futex, RESOURCE, FUTEX_WAKE, 1, NULL, NULL, 0); \

An unconditional syscall in the wake path? I'm pretty sure that will make it slower than pthread mutex.

I completely agree with benchmarking and testing this thing before de-drafting it. I don't trust eyeball measurements for this kind of stuff, I suspect they'll measure mostly placebo.