Re: [Intel-gfx] [igt-dev] [PATCH i-g-t 3/4] i915/gem_create: use __atomic_* instead of __sync_*

Ser, Simon
2019-06-06T07:20:23Z

On Mon, 2019-06-03 at 12:54 +0100, Guillaume Tucker wrote:
> Replace calls to the older __sync_* functions with the new __atomic_*
> standard ones. This fixes builds on some architectures, in particular
> MIPS which doesn't have __sync_add_and_fetch_8 and
> __sync_val_compare_and_swap_8 for 64-bit variable handling.

Can't we use the C11 atomics from stdatomic.h instead?

For instance:
https://en.cppreference.com/w/c/atomic/atomic_compare_exchange

> Signed-off-by: Guillaume Tucker <guillaume.tucker@collabora.com>
> ---
> tests/Makefile.am | 2 +-
> tests/i915/gem_create.c | 12 ++++++++++--
> 2 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/tests/Makefile.am b/tests/Makefile.am
> index 5097debf629c..18a0f1f20592 100644
> --- a/tests/Makefile.am
> +++ b/tests/Makefile.am
> @@ -90,7 +90,7 @@ AM_LDFLAGS = -Wl,--as-needed
> drm_import_export_CFLAGS = $(AM_CFLAGS) $(THREAD_CFLAGS)
> drm_import_export_LDADD = $(LDADD) -lpthread
> gem_create_CFLAGS = $(AM_CFLAGS) $(THREAD_CFLAGS)
> -gem_create_LDADD = $(LDADD) -lpthread
> +gem_create_LDADD = $(LDADD) -lpthread -latomic
> gem_close_race_CFLAGS = $(AM_CFLAGS) $(THREAD_CFLAGS)
> gem_close_race_LDADD = $(LDADD) -lpthread
> gem_ctx_thrash_CFLAGS = $(AM_CFLAGS) $(THREAD_CFLAGS)
> diff --git a/tests/i915/gem_create.c b/tests/i915/gem_create.c
> index 43cbf45f289b..a4aeb94b3f93 100644
> --- a/tests/i915/gem_create.c
> +++ b/tests/i915/gem_create.c
> @@ -156,6 +156,14 @@ static void invalid_nonaligned_size(int fd)
> gem_close(fd, create.handle);
> }
>
> +static uint64_t atomic_compare_swap_u64(uint64_t *ptr, uint64_t oldval,
> + uint64_t newval)
> +{
> + __atomic_compare_exchange_n(ptr, &oldval, newval, 0,
> + __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
> + return oldval;
> +}
> +
> static uint64_t get_npages(uint64_t *global, uint64_t npages)
> {
> uint64_t try, old, max;
> @@ -165,7 +173,7 @@ static uint64_t get_npages(uint64_t *global, uint64_t npages)
> old = max;
> try = 1 + npages % (max / 2);
> max -= try;
> - } while ((max = __sync_val_compare_and_swap(global, old, max)) != old);
> + } while ((max = atomic_compare_swap_u64(global, old, max)) != old);
>
> return try;
> }
> @@ -202,7 +210,7 @@ static void *thread_clear(void *data)
> }
> gem_close(i915, create.handle);
>
> - __sync_add_and_fetch(&arg->max, npages);
> + __atomic_add_fetch(&arg->max, npages, __ATOMIC_SEQ_CST);
> }
>
> return NULL;
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