On Fri, Dec 15, 2017 at 8:27 AM, Chris Wilson <ch...@chris-wilson.co.uk>
wrote:
> 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.
>
So a second open() of /dev/dri/card0 will get a different default context?
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