On Fri, Oct 21, 2016 at 08:21:08AM +0100, Tvrtko Ursulin wrote: > > On 20/10/2016 21:36, Chris Wilson wrote: > >On Thu, Oct 20, 2016 at 05:22:23PM +0100, Tvrtko Ursulin wrote: > >> > >>On 20/10/2016 16:03, Chris Wilson wrote: > >>>Quite a few of our objects used for internal hardware programming do not > >>>benefit from being swappable or from being zero initialised. As such > >>>they do not benefit from using a shmemfs backing storage and since they > >>>are internal and never directly exposed to the user, we do not need to > >>>worry about providing a filp. For these we can use an > >>>drm_i915_gem_object wrapper around a sg_table of plain struct page. They > >>>are not swap backed and not automatically pinned. If they are reaped > >>>by the shrinker, the pages are released and the contents discarded. For > >>>the internal use case, this is fine as for example, ringbuffers are > >>>pinned from being written by a request to be read by the hardware. Once > >>>they are idle, they can be discarded entirely. As such they are a good > >>>match for execlist ringbuffers and a small variety of other internal > >>>objects. > >>> > >>>In the first iteration, this is limited to the scratch batch buffers we > >>>use (for command parsing and state initialisation). > >> > >>And the status page. > > > >Yeah, I was just thinking of the runtime allocated blocks where the > >change can be measured. > > > >>>+ max_order = MAX_ORDER; > >>>+#ifdef CONFIG_SWIOTLB > >>>+ if (swiotlb_nr_tbl()) > >>>+ max_order = min(max_order, ilog2(IO_TLB_SEGSIZE)); > >>>+#endif > >> > >>I couldn't figure out what IO_TLB_SEGSIZE actually is in some > >>minutes of cross-referencing. Did not seem to be in units of bytes > >>according to swiotlb.h. > > > >Pages. > > > >>In either case my question is - why use different parameters than > >>swiotlb_max_size you recently added to i915_gem.c? > > > >I was trying to exploit the compile time constants, and I did not care > >to grow the search for even higher orders. > > Sorry pages, but it is not AFAICS, but it is units of IO_TLB_SHIFT > size which is 2k. Happens to be fine since it is smaller (5) than > MAX_ORDER (11), however to me it still looks like a unrelated > number. > > ilog2(IO_TLB_SEGSIZE) + 1 would be the same units. It would still > look arbitrary but I suppose it would be passable. Oh, no! I do remember that. I guess that shows the importance of comments since I lost that fact during the chase to find a way of writing fls() as a compiletime constant. Let's /* convert swiotlb segment size into sensible units! */ #define IO_TLB_SEGPAGES (IO_TLB_SEGSIZE << IO_TLB_SHIFT >> PAGE_SHIFT) -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
