On Mon, May 7, 2012 at 1:59 PM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote: >> On 07.05.2012 17:23, Jerome Glisse wrote: >>> >>> On Mon, May 7, 2012 at 7:42 AM, Christian König<deathsimple@xxxxxxxxxxx> >>> wrote: >>>> >>>> A startover with a new idea for a multiple ring allocator. >>>> Should perform as well as a normal ring allocator as long >>>> as only one ring does somthing, but falls back to a more >>>> complex algorithm if more complex things start to happen. >>>> >>>> We store the last allocated bo in last, we always try to allocate >>>> after the last allocated bo. Principle is that in a linear GPU ring >>>> progression was is after last is the oldest bo we allocated and thus >>>> the first one that should no longer be in use by the GPU. >>>> >>>> If it's not the case we skip over the bo after last to the closest >>>> done bo if such one exist. If none exist and we are not asked to >>>> block we report failure to allocate. >>>> >>>> If we are asked to block we wait on all the oldest fence of all >>>> rings. We just wait for any of those fence to complete. >>>> >>>> v2: We need to be able to let hole point to the list_head, otherwise >>>> try free will never free the first allocation of the list. Also >>>> stop calling radeon_fence_signalled more than necessary. >>>> >>>> Signed-off-by: Christian König<deathsimple@xxxxxxxxxxx> >>>> Signed-off-by: Jerome Glisse<jglisse@xxxxxxxxxx> >>> >>> This one is NAK please use my patch. Yes in my patch we never try to >>> free anything if there is only on sa_bo in the list if you really care >>> about this it's a one line change: >>> >>> http://people.freedesktop.org/~glisse/reset5/0001-drm-radeon-multiple-ring-allocator-v2.patch >> >> Nope that won't work correctly, "last" is pointing to the last allocation >> and that's the most unlikely to be freed at this time. Also in this version >> (like in the one before) radeon_sa_bo_next_hole lets hole point to the >> "prev" of the found sa_bo without checking if this isn't the lists head. >> That might cause a crash if an to be freed allocation is the first one in >> the buffer. >> >> What radeon_sa_bo_try_free would need to do to get your approach working is >> to loop over the end of the buffer and also try to free at the beginning, >> but saying that keeping the last allocation results in a whole bunch of >> extra cases and "if"s, while just keeping a pointer to the "hole" (e.g. >> where the next allocation is most likely to succeed) simplifies the code >> quite a bit (but I agree that on the down side it makes it harder to >> understand). >> >>> Your patch here can enter in infinite loop and never return holding >>> the lock. See below. >>> >>> [SNIP] >>> >>>> + } while (radeon_sa_bo_next_hole(sa_manager, fences)); >>> >>> Here you can infinite loop, in the case there is a bunch of hole in >>> the allocator but none of them allow to full fill the allocation. >>> radeon_sa_bo_next_hole will keep returning true looping over and over >>> on all the all. That's why i only restrict my patch to 2 hole skeeping >>> and then fails the allocation or try to wait. I believe sadly we need >>> an heuristic and 2 hole skeeping at most sounded like a good one. >> >> Nope, that can't be an infinite loop, cause radeon_sa_bo_next_hole in >> conjunction with radeon_sa_bo_try_free are eating up the opportunities for >> holes. >> >> Look again, it probably will never loop more than RADEON_NUM_RINGS + 1, with >> the exception for allocating in a complete scattered buffer, and even then >> it will never loop more often than halve the number of current allocations >> (and that is really really unlikely). >> >> Cheers, >> Christian. > > I looked again and yes it can loop infinitly, think of hole you can > never free ie radeon_sa_bo_try_free can't free anything. This > situation can happen if you have several thread allocating sa bo at > the same time while none of them are yet done with there sa_bo (ie > none have call sa_bo_free yet). I updated a v3 that track oldest and > fix all things you were pointing out above. > > http://people.freedesktop.org/~glisse/reset5/0001-drm-radeon-multiple-ring-allocator-v3.patch > > Cheers, > Jerome Of course by tracking oldest it defeat the algo so updated patch : http://people.freedesktop.org/~glisse/reset5/0001-drm-radeon-multiple-ring-allocator-v3.patch Just fix the corner case of list of single entry. Cheers, Jerome _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
