On Tue, Nov 25, 2014 at 04:42:22PM +0000, Daniel, Thomas wrote: > > -----Original Message----- > > From: Daniel Vetter [mailto:daniel.vetter@xxxxxxxx] On Behalf Of Daniel > > Vetter > > Sent: Tuesday, November 25, 2014 4:00 PM > > To: Chris Wilson; Daniel, Thomas; Daniel Vetter; intel- > > gfx@xxxxxxxxxxxxxxxxxxxxx; akash goel (akash.goels@xxxxxxxxx) > > Subject: Re: [PATCH] drm/i915: Don't pin LRC in GGTT when > > dumping in debugfs > > > > On Tue, Nov 25, 2014 at 02:44:33PM +0000, Chris Wilson wrote: > > > On Tue, Nov 25, 2014 at 02:30:55PM +0000, Daniel, Thomas wrote: > > > > > -----Original Message----- > > > > > From: daniel.vetter@xxxxxxxx [mailto:daniel.vetter@xxxxxxxx] On > > > > > Behalf Of Daniel Vetter > > > > > Sent: Thursday, November 20, 2014 12:51 PM > > > > > To: Chris Wilson; Daniel, Thomas; intel-gfx@xxxxxxxxxxxxxxxxxxxxx; > > > > > akash goel > > > > > (akash.goels@xxxxxxxxx) > > > > > Subject: Re: [PATCH] drm/i915: Don't pin LRC in GGTT > > > > > when dumping in debugfs > > > > > > > > > > On Thu, Nov 20, 2014 at 1:28 PM, Chris Wilson > > > > > <chris@xxxxxxxxxxxxxxxxxx> > > > > > wrote: > > > > > >> Can you identify any situation where the pages may go away? > > > > > > > > > > > > Anytime you trigger an allocation, the system may reap any > > > > > > objects pages. It will even steal the dev->struct_mutex. To > > > > > > protect against the shrinker you have to call pin_pages(). Here, > > > > > > there are no allocations inside the loop and so you don't need > > > > > > to worry about the shrinker stealing your pages. > > > > > > > > > > Hm actually I think better safe than sorry here. At least I have > > > > > (again) completely forgotten about our dear shrinker ... > > > > > -Daniel > > > > > > > > Does this discussion count as a review? What was the conclusion - do I > > need to make a version without pinning or is it better safe than sorry? > > > > > > To bring it full circle: > > > > > > >> LRC object does not need to be mapped into the GGTT when dumping. > > > >> Just use pin_pages. A side-effect of this patch is that a compiler > > > >> warning goes away (not checking return value of > > i915_gem_obj_ggtt_pin). > > > > > > > Please explain why you need to pin the pages. > > > > > > In particular, explain why just calling pin_pages() doesn't do what > > > you want. And then afterwards you can leave a note in the commitlog > > > why you use pin_pages() as overkill. > > > > Ok I think I see the confusion - we still don't have any error checking, > > because we don't call get_pages. pin_pages alone doesn't do a whole lot > > really. We might actually want to put the get_pages into the pin_pages to > > simplify the interface a bit. Well we need to keep the raw version as __ since > > some users really don't want a get_pages. > > -Daniel > Well I'm more confused now. Pin_pages() just increments a refcount. There should already be backing store allocated as the context is in the dev_priv->context_list and we have the struct_mutex. The code calls i915_gem_object_get_page to get a pointer to page 1 of the context object (the logical ring context is here), then kmaps it. What is the benefit of calling get_pages? Do you mean i915_gem_object_ops.get_pages? I don't care if the object is mapped into GTT at this point - I just want to dump it from the CPU. That's why I removed the ggtt_pin in the first place. The object does not necessarily have any obj->pages at this point. i915_gem_object_get_pages() returns NULL and the code OOPSes. -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
