Quoting Jason Ekstrand (2017-12-15 16:21:42)
> On Fri, Dec 15, 2017 at 5:42 AM, Chris Wilson <ch...@chris-wilson.co.uk>
> wrote:
>
> Every client (everyone instance that opens /dev/dri/card0 or the render
> nodes), receives a unique per-process GTT (where supported by the
> hardware, unfortunately that means only Broadwell and later). Every
> context created by each client, in turns receives its own unique ppGTT.
> This is overkill in terms of allocations and tracking, both in the
> kernel and in the hardware, as we could be sharing the per-client GTT
> amongst all of its contexts. The downside is that context segregation is
> reduced, a stray write from one context may affect another, and so we
> must honour any client requests that require robust segregation (e.g.
> ARB_robustness).
>
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> ---
> src/mesa/drivers/dri/i965/brw_bufmgr.c | 23 +++++++++++++++++------
> src/mesa/drivers/dri/i965/brw_bufmgr.h | 2 +-
> src/mesa/drivers/dri/i965/brw_context.c | 2 +-
> 3 files changed, 19 insertions(+), 8 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_bufmgr.c
> b/src/mesa/drivers/dri/
> i965/brw_bufmgr.c
> index 52b5bf97a1..d8a9635f5d 100644
> --- a/src/mesa/drivers/dri/i965/brw_bufmgr.c
> +++ b/src/mesa/drivers/dri/i965/brw_bufmgr.c
> @@ -1297,13 +1297,24 @@ init_cache_buckets(struct brw_bufmgr *bufmgr)
> }
>
> uint32_t
> -brw_create_hw_context(struct brw_bufmgr *bufmgr)
> +brw_create_hw_context(struct brw_bufmgr *bufmgr, unsigned int flags)
> {
> - struct drm_i915_gem_context_create create = { };
> - int ret = drmIoctl(bufmgr->fd, DRM_IOCTL_I915_GEM_CONTEXT_CREATE, &
> create);
> - if (ret != 0) {
> - DBG("DRM_IOCTL_I915_GEM_CONTEXT_CREATE failed: %s\n", strerror
> (errno));
> - return 0;
> + struct local_i915_gem_context_create_v2 {
> + uint32_t ctx_id; /* out */
> + uint32_t flags;
> +#define I915_GEM_CONTEXT_SHARE_GTT 0x1
> + uint32_t share_ctx;
>
>
> So, we've left share_ctx as 0. What does that mean? Does that mean that we
> share with some context that was implicitly created by opening
> /dev/dri/card0?
> Does it mean we share with the default context and therefore other processes?
The default context, 0, is per fd.
-Chris
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