On 11/29/2012 03:15 AM, Marek Ol??k wrote: > On Thu, Nov 29, 2012 at 12:44 AM, Alan Swanson <swanson at ukfsn.org> wrote: >> On Wed, 2012-11-28 at 18:24 -0500, Jerome Glisse wrote: >>> On Wed, Nov 28, 2012 at 6:18 PM, Thomas Hellstrom <thomas at shipmail.org> >>> wrote: >>>> On 11/28/2012 04:58 PM, j.glisse at gmail.com wrote: >>>>> From: Jerome Glisse <jglisse at redhat.com> >>>>> >>>>> This patch add a minimum residency time configurable for each memory >>>>> pool (VRAM, GTT, ...). Intention is to avoid having a lot of memory >>>>> eviction from VRAM up to a point where the GPU pretty much spend all >>>>> it's time moving things in and out. >>>> >>>> This patch seems odd to me. >>>> >>>> It seems the net effect is to refuse evictions from VRAM and make buffers >>>> go >>>> somewhere else, and that makes things faster? >>>> >>>> Why don't they go there in the first place instead of trying to force them >>>> into VRAM, >>>> when VRAM is full? >>>> >>>> /Thomas >>> It's mostly a side effect of cs and validating with each cs, if boA is >>> in cs1 and not in cs2 and boB is in cs1 but not in cs2 than boA could >>> be evicted by cs2 and boB moved in, if next cs ie cs3 is like cs1 then >>> boA move back again and boB is evicted, then you get cs4 which >>> reference boB but not boA, boA get evicted and boB move in ... So ttm >>> just spend its time doing eviction but he doing so because it's ask by >>> the driver to do so. Note that what is costly there is not the bo move >>> in itself but the page allocation. >>> >>> I propose this patch to put a boundary on bo eviction frequency, i >>> thought it might help other driver, if you set the residency time to 0 >>> you get the current behavior, if you don't you enforce a minimum >>> residency time which helps driver like radeon. Of course a proper fix >>> to the bo eviction for radeon has to be in radeon code and is mostly >>> an overhaul of how we validate bo. >>> >>> But i still believe that this patch has value in itself by allowing >>> driver to put a boundary on buffer movement frequency. >>> >>> Cheers, >>> Jerome >> So, a variation on John Carmack's recommendation from 2000 to use MRU, >> not LRU, to avoid texture trashing. >> >> Mar 07, 2000 - Virtualized video card local memory is The Right Thing. >> http://floodyberry.com/carmack/johnc_plan_2000.html >> >> In fact, this was last discussed in 2005 with a patch for a 1 second >> stale texture eviction and I (still) wondered why a method it was never >> implemented since it was an clear problem. > BTW we can send end-of-frame markers to the kernel, which could be > used to implement Carmack's algorithm. > > Marek
It seems to me like Carmack's algorithm is quite specific to the case where only a single GL client is running? It also seems like it's designed around the fact that when eviction takes place, all buffer objects will be idle. With a reasonably filled graphics fifo / ring, blindly using MRU will cause the GPU to run synchronized. /Thomas > _______________________________________________ > dri-devel mailing list > dri-devel at lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/dri-devel
