Here's a blend which renders (coincidentally) 2.7x slower when using progressive refine: http://gregzaal.com/ss/progressive_refine_speed.blend (44 MB)
Rendering on GPU - 2x gtx 570, win7 64 bit, blender 2.72.2 (5cce2e1) Progressive refine off: 139 seconds Progressive refine on: 377 seconds Render res: 1200x1400 (tile size: 240x234, top to bottom) Cheers, Greg On 13 November 2014 12:49, Sergey Sharybin <[email protected]> wrote: > Brecht, it's multiple factors being involved here, starting from CPU cache > coherence issues (which we can't easily predict) ending with less efficient > buffers update (we might be saving all the passes after each of the samples > in case of progressive refine, which we can fix). > > But yeah, should have asked for a demo file in the original file :) So do > you guys have a demo .blend file which demonstrates such a major slowdown? > > Brecht, we can (and actually should) do several samples per tile, but i'd > prefer log(). not sqrt() perhaps. Other idea to improve cache coherence > would be to use left-to-right, bottom-to-top tile scheduling. That gives > few %% of speedup, and AFAIR we don't fallback to such a scheduling in > progressive refine. > > And even after the tweaks, we should probably replace "somewhat" to > something more deterministic in the tooltip. > > On Thu, Nov 13, 2014 at 10:58 AM, Brecht Van Lommel < > [email protected]> wrote: > > > If it is really 100% or 300% slower then that sounds like a fixable > issue. > > > > I'm not sure why it would be this slow, it would be good to find out why, > > but one thing that would speed it up is to render more samples at a the > > time and redraw less often as the current sample increases. Due to the > way > > Monte Carlo integration works, one sample barely makes any visible > > difference in noise after a while anyway. > > > > Maybe something like: > > num_samples_at_once = sqrt(max(current_sample - 4, 1)) > > On Nov 13, 2014 10:13 AM, "Greg Zaal" <[email protected]> wrote: > > > > Just by the way, it's even more noticeable with GPU rendering - I've seen > > it roughly 300% slower often. > > > > "could lead to significant slowdown" sounds good to me. > > > > On 13 November 2014 11:06, Sergey Sharybin <[email protected]> wrote: > > > > > The issue here is that basically slowdown depends on particular > hardware > > > configuration, tile settings and device used to render (GPU/CPU). > > Meaning, > > > on modern CPU i've noticed around 20% slowdown peak, which is not that > > bad > > > as 100%. So what i'm trying to say here, is that if we'll provide > > > information "up to 100% slower" it might just scary artists and they > > > wouldn't use the option at all, even though for their configuration > > > slowdown wouldn't be so bad. > > > > > > What about more neutral (in my opinion): "could lead to significant > > > slowdown"? > > > > > > On Thu, Nov 13, 2014 at 12:22 AM, Simon Repp <[email protected]> > > > wrote: > > > > > > > Dear Renderistas, > > > > > > > > I only recently found out that progressive refinement in Cycles > > > > rendering (which the corresponding checkbox's tooltip describes to be > > > > "somewhat slower" than bucket rendering) in fact can impose > performance > > > > penalties of over 100% (aka the same amount of samples takes more > than > > > > twice as long to render). > > > > > > > > Now I don't know if this is just a personal flawed interpretation of > > the > > > > english language on my part, but when reading "somewhat slower" I > > didn't > > > > realize what I was really in for, and in retrospect I'd rather not > > > > reconstruct how many days my poor laptop spent in excess to render > some > > > > projects I did in the past. > > > > > > > > I'd hereby like to propose a change of this tooltip to something less > > > > ambiguous, lest anyone else falls into that same trap that I have - > My > > > > proposal for this would be to include actual figures describing the > > > > possible speed penalty that progressive refinement can impose, that > is, > > > > something along the lines of "renders [a]% to [b]% slower depending > on > > > > the scene", where figures [a] and [b] are ideally derived from real > > > > world data we gather (or already have?) about how much speed penalty > > > > progressive refinement can impose in different scenes. Alternatively, > > > > only stating "up to [x]% slower" would work as well I guess, as the > > main > > > > point is to make people aware that it _can_ possibly affect render > > times > > > > _significantly_. > > > > > > > > If the proposal to include figures is not agreeable for some reason, > I > > > > would at least ask for a more indicative wording than "somewhat > > slower", > > > > which even after consulting multiple dictionaries I'm not sure if > there > > > > is an official interpretation for. (One dictionary suggests "quite" > as > > a > > > > synoym, another "slightly" ...) I'd still prefer the figures though, > no > > > > one looks up terms in the dictionary while using Blender and I am > > > > probably not the worst offender at massacring and misunderstanding > the > > > > english language in the Blender community, and it doesn't get less > > > > ambiguous than numbers anyway, so I say we use them here? :) > > > > > > > > Best, > > > > Simon > > > > _______________________________________________ > > > > Bf-committers mailing list > > > > [email protected] > > > > http://lists.blender.org/mailman/listinfo/bf-committers > > > > > > > > > > > > > > > > -- > > > With best regards, Sergey Sharybin > > > _______________________________________________ > > > Bf-committers mailing list > > > [email protected] > > > http://lists.blender.org/mailman/listinfo/bf-committers > > > > > _______________________________________________ > > Bf-committers mailing list > > [email protected] > > http://lists.blender.org/mailman/listinfo/bf-committers > > _______________________________________________ > > Bf-committers mailing list > > [email protected] > > http://lists.blender.org/mailman/listinfo/bf-committers > > > > > > -- > With best regards, Sergey Sharybin > _______________________________________________ > Bf-committers mailing list > [email protected] > http://lists.blender.org/mailman/listinfo/bf-committers > _______________________________________________ Bf-committers mailing list [email protected] http://lists.blender.org/mailman/listinfo/bf-committers
