SoC 2008/x264/Speed Optimizations

This project is part of Google Summer of Code 2008. Student: Holger Lubitz Mentor: Alex Izvorski

Project Abstract

My goal is to search for speed optimizations in x264 (and, time allowing or if anything seems an obvious port, possibly a bit in vlc and ffmpeg as well). I intend to thouroughly profile the thing and find out where we might do better.

Implementation

Will be mainly on a day to day basis - find something, see if something can be done about it. My main development system so far was an Athlon X2 3800+, so I mainly did 64bit and MMX, some SSE code so far, but it recently lost its case to a new and shiny Q9300 (will be back in service once that case arrives - seems it may take a while). I intend to be learning a lot of SSSE3 and SSE4.1 and will hopefully find some uses for it.

Current Status

Battling with Hardware. Fedora 9 is said to have the latest and greatest of all distributions in regard to supporting the Intel Onboard-Graphics (it's just a little bit behind on the version number and i think most of the newer stuff is already in). However, my G35 mobo does not really like me yet. Some things still to be found out. Expect me to rant a bit on the channel if it was just another really bad day.

Other than that, I hope to get into vtune next week, maybe even try to get the free IDA going somehow. And then we'll see where that gets me.

Week 1

Downloaded free IDA 4.9 and demo version of 5.2. The free version works surprisingly well in current wine. Just some font problems (fixed by selecting another one) and window handling is a bit awkward sometimes. Successfully disassembled some linux programs. Unfortunately the free version doesn't do 64 bit code and newer SSE, and the demo is severely limited in other aspects (no saves, time limit per session).

But then again, so far good old objconv -fasm worked well enough, too. So IDA should be nice to have if needed.

Registered with Intel for non-commercial downloads and got Intel Compiler Collection, Performance Primitives and of course vtune, but vtune officially only supports Fedora up to 7 (and with stock kernel) currently. Will have to fiddle a bit with that in the next days (given the X problems I had even with the current driver, downgrading to 7 is probably not even an option).

Found out about liboil and checked their zigzag implementation. They have an altivec zigzag, but it doesn't look like their idea can be borrowed - ends with a lot of fixup in c. But I think checking there for other ideas cannot hurt. Will keep a copy.

Hardware troubles turned out to be partly hardware, partly software related. Both 4 GB kits have been faulty (either A-Data Vitesta wasn't the best brand to buy or it was just my sheer luck again that both gave errors in memtest86). Returned them, hope the vendor is going to refund the money soon. Running on the 4x1 GB from my previous system for the time being. X currently only works with uncached video memory. Shouldn't affect the encoding measurements, however I noted that h264 playback becomes very jerky with uncached memory. Fedora already has an open bug for the issue - let's hope it can be resolved soon.

Week 2

Some initial profiling next. Dark_Shikari suggested using his Black Pearl clip for that. Open to suggestions for suitable HD material. Going to use Elephants Dream if nothing better comes up. Will also try to find out if there are notable differences with interlaced material (will use DVB-S captures for that, probably a bit of Torchwood).

After that, submit at least my qualification patches to git. And see if that SSE2 zigzag goes anywhere on core. Will also be first experience with the dreaded cacheline issues ;)

Schedule

Had a presentation on May 23rd (yeah, just the right time to buy and install new hardware). Will need to hand in the write up for all of it soonish. After that, mainly weather dependent. Cold heads code, hot heads need to be near (preferably cold) water. Well. Wasn't coding what nights were made for?

Been to my professors office hour Jun 2. Paper on the presentation (or rather, the term project presented) due Jun 6. Right in time for Euro 2008 ;) No, honestly: After that, mostly clear skies ahead time-wise. (Except maybe a bit of footy plus poker every now and then. Let's see how Germany does :)

Other probable time constraints: Will have to juggle a bit between doing things for GSoC and thinking (and writing) about these things for my Thesis. Switching sometimes should help keep up motivation (and idea flow) for the other. Otherwise, nothing largish. Maybe a weekend trip or two, but nothing long lasting.

May 31/Jun 1: Visit family. (Nice visit. Sister dropped by on her trip back from UK to Australia, and saw my oldest aunt again after >8 years. Sunny weather, unusually hot for the time of year. Usually, we only see >30C in August, if at all. Hope it'll get a bit colder soon.)