Quoting Kenneth Graunke (2017-09-08 08:19:03) > On Wednesday, September 6, 2017 8:44:03 AM PDT Chris Wilson wrote: > > Quoting Kenneth Graunke (2017-09-06 16:20:00) > > > On Wednesday, September 6, 2017 3:08:44 AM PDT Chris Wilson wrote: > > > > Quoting Kenneth Graunke (2017-09-06 01:09:47) > [snip] > > > > > +/* Don't exceed this - batchbuffers need to fit in the ring! */ > > > > > > > > I don't understand this comment. I probably just have the wrong pov, you > > > > say ring and I then think of the legacy/lrc ringbuffer in the kernel. > > > > > > My understanding was that the legacy Gen4-7.5 ringbuffer mode allocated a > > > ringbuffer that was...128kB large? So if you exceeded that size, the > > > batch would not fit in the ring at all, and execbuf would fail. > > > > We don't copy the batch into the ring, we just stick a > > MI_BATCH_BUFFER_START in there (with a flush before/after and a > > breadcrumb, along with any context switch, change of mm, etc). > > Oh, right...so that doesn't make sense. > > > 64k is indeed a magic limit for the state batch though, but as there's > > What causes this limit?
Surface state is limited to 64k "elements". You would think that element applies to the 32 byte descriptor, but empirically if you reference a sampler beyond the 64k byte, it returns all 0. > > no limit on the batch buffer size (after converting it to a pure command > > stream, just the prospect of a timeout). Well... There is an implicit > > assumption that you don't exceed 256KiB for a batch (as a limit for a gen2 > > workaround and a different gen7 workaround). > > > > Elsewhere, I have used 256KiB batches (and then shrunk to fit) simply > > because of UINT16_MAX dwords. (Which is kind of why the kernel assumes > > that the upper reasonable maximum size is 256KiB for its w/a.) > > Should I change this to 256kB then? If you want an upper bound, sure. I don't think you have any plans that require the kernel to care about your batchbuffer size :) -Chris _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
