[Mesa-dev] [PATCH 3/6] amd/common: Add detection of the syncobj wait/signal/reset ioctls.

[Bas Nieuwenhuizen]

For vulkan, I wanted this because of

drm/syncobj: Allow wait for submit and signal behavior (v5)

    Vulkan VkFence semantics require that the application be able to perform
    a CPU wait on work which may not yet have been submitted.  This is
    perfectly safe because the CPU wait has a timeout which will get
    triggered eventually if no work is ever submitted.  This behavior is
    advantageous for multi-threaded workloads because, so long as all of the
    threads agree on what fences to use up-front, you don't have the extra
    cross-thread synchronization cost of thread A telling thread B that it
    has submitted its dependent work and thread B is now free to wait.

    Within a single process, this can be implemented in the userspace driver
    by doing exactly the same kind of tracking the app would have to do
    using posix condition variables or similar.  However, in order for this
    to work cross-process (as is required by VK_KHR_external_fence), we need
    to handle this in the kernel.

    This commit adds a WAIT_FOR_SUBMIT flag to DRM_IOCTL_SYNCOBJ_WAIT which
    instructs the IOCTL to wait for the syncobj to have a non-null fence and
    then wait on the fence.  Combined with DRM_IOCTL_SYNCOBJ_RESET, you can
    easily get the Vulkan behavior.


I suppose you could use an earlier DRM version if you don't need it.
IMO we should keep them separate, as on radv semaphores don't need any
wait functionality at all.

On Tue, Dec 26, 2017 at 6:29 PM, Marek Olšák <maraeo at gmail.com> wrote:
> Does this mean that radeonsi shouldn't use amdgpu_cs_syncobj_wait on older DRM?
>
> Does it make sense to have separate has_syncobj and has_syncobj_wait flags?
>
> Marek
>
> On Sun, Dec 17, 2017 at 1:11 AM, Bas Nieuwenhuizen
> <bas at basnieuwenhuizen.nl> wrote:
>> First amdgpu bump after inclusion was 20 (which was done for local BOs).
>> ---
>>  src/amd/common/ac_gpu_info.c | 1 +
>>  src/amd/common/ac_gpu_info.h | 1 +
>>  2 files changed, 2 insertions(+)
>>
>> diff --git a/src/amd/common/ac_gpu_info.c b/src/amd/common/ac_gpu_info.c
>> index 0576dd369cf..c042bb229ce 100644
>> --- a/src/amd/common/ac_gpu_info.c
>> +++ b/src/amd/common/ac_gpu_info.c
>> @@ -277,6 +277,7 @@ bool ac_query_gpu_info(int fd, amdgpu_device_handle dev,
>>                 vce.available_rings ? vce_version : 0;
>>         info->has_userptr = true;
>>         info->has_syncobj = has_syncobj(fd);
>> +       info->has_syncobj_wait = info->has_syncobj && info->drm_minor >= 20;
>>         info->has_sync_file = info->has_syncobj && info->drm_minor >= 21;
>>         info->has_ctx_priority = info->drm_minor >= 22;
>>         info->num_render_backends = amdinfo->rb_pipes;
>> diff --git a/src/amd/common/ac_gpu_info.h b/src/amd/common/ac_gpu_info.h
>> index 5b9e51658b0..04e17f91c59 100644
>> --- a/src/amd/common/ac_gpu_info.h
>> +++ b/src/amd/common/ac_gpu_info.h
>> @@ -81,6 +81,7 @@ struct radeon_info {
>>         uint32_t                    drm_patchlevel;
>>         bool                        has_userptr;
>>         bool                        has_syncobj;
>> +       bool                        has_syncobj_wait;
>>         bool                        has_sync_file;
>>         bool                        has_ctx_priority;
>>
>> --
>> 2.15.1
>>
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