Re: [PATCH] intel: Delay testing for userptr until first use

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 11/04/2014 02:31 PM, Chris Wilson wrote:
> Running __mmu_notifier_register() is surprisingly expensive, so let's
> not do that unless we have to.

Affects some program startup or what? What is the cost? I would add some 
notes in the commit for future reference.

> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   intel/intel_bufmgr_gem.c | 114 +++++++++++++++++++++++++++--------------------
>   1 file changed, 65 insertions(+), 49 deletions(-)
>
> diff --git a/intel/intel_bufmgr_gem.c b/intel/intel_bufmgr_gem.c
> index f2f4fea..addf413 100644
> --- a/intel/intel_bufmgr_gem.c
> +++ b/intel/intel_bufmgr_gem.c
> @@ -935,6 +935,70 @@ drm_intel_gem_bo_alloc_userptr(drm_intel_bufmgr *bufmgr,
>   	return &bo_gem->bo;
>   }
>
> +static bool
> +has_userptr(drm_intel_bufmgr_gem *bufmgr_gem)
> +{
> +	int ret;
> +	void *ptr;
> +	long pgsz;
> +	struct drm_i915_gem_userptr userptr;
> +	struct drm_gem_close close_bo;
> +
> +	pgsz = sysconf(_SC_PAGESIZE);
> +	assert(pgsz > 0);
> +
> +	ret = posix_memalign(&ptr, pgsz, pgsz);
> +	if (ret) {
> +		DBG("Failed to get a page (%ld) for userptr detection!\n",
> +			pgsz);
> +		return false;
> +	}
> +
> +	memset(&userptr, 0, sizeof(userptr));
> +	userptr.user_ptr = (__u64)(unsigned long)ptr;
> +	userptr.user_size = pgsz;
> +
> +retry:
> +	ret = drmIoctl(bufmgr_gem->fd, DRM_IOCTL_I915_GEM_USERPTR, &userptr);
> +	if (ret) {
> +		if (errno == ENODEV && userptr.flags == 0) {
> +			userptr.flags = I915_USERPTR_UNSYNCHRONIZED;
> +			goto retry;
> +		}
> +		free(ptr);
> +		return false;
> +	}
> +
> +	close_bo.handle = userptr.handle;
> +	ret = drmIoctl(bufmgr_gem->fd, DRM_IOCTL_GEM_CLOSE, &close_bo);
> +	free(ptr);
> +	if (ret) {
> +		fprintf(stderr, "Failed to release test userptr object! (%d) "
> +				"i915 kernel driver may not be sane!\n", errno);
> +		return false;
> +	}
> +
> +	return true;
> +}
> +
> +static drm_intel_bo *
> +check_bo_alloc_userptr(drm_intel_bufmgr *bufmgr,
> +		       const char *name,
> +		       void *addr,
> +		       uint32_t tiling_mode,
> +		       uint32_t stride,
> +		       unsigned long size,
> +		       unsigned long flags)
> +{
> +	if (has_userptr((drm_intel_bufmgr_gem *)bufmgr))
> +		bufmgr->bo_alloc_userptr = drm_intel_bo_alloc_userptr;

I wouldn't have spotted this - so retroactively compile tested I assume?

Otherwise,
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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