Category Archives: Computers

SC13 Retrospective

Posted on 2014-01-02 by pappp

Posting up my notes from SC13 is another thing I didn’t get to during the end of the semester. Remedying now.

The main takeaway sequence from conversations on the floor is as such:

  1. The era of single-core performance gains is already over.
  2. Furthermore, the era of usable single-die performance for MIMD machines is coming to an end.
  3. Therefore, big machines are going to be getting physically bigger… to the point where connection lengths are a problem (everything is Infiniband, and Infiniband doesn’t tolerate long runs well)
  4. There is a LOT of cooling effort to make the necessary density happen – central large fan systems, immersion cooling, closed-circuit water gear, etc.

The other really exciting thing that it seems AMD is going to make it, and more. Their lean period finished when the payoff on the XBone/PS4 came in, and they have a VERY good plan for the next >2 years. It works with the premise above about single-core/die MIMD performance ending, and points in the HSA direction – this is the crazy parts with MMUs so a CPU and GPU can share memory without skew penalty and such. ARM and partners are also generally pointed that way, and have been for some time, though apparently AMD isn’t getting out of the x86 game, but it does look like they are getting out of the fat core game.
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Hosting Move

Posted on 2013-12-24 by pappp

I’ve just completed a move of this site to a new host, it should be transparent to everyone else – modulo a few brief intervals during the move – so please let me know if anything appears broken. There is also an exciting new feature in that (almost) everything should now be accessible via SSL. Notes on vendors and selections below the fold.

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Heterogeneous System Architecture

Posted on 2013-11-23 by pappp

Post-SC, I sat down to do some deeper reading on the HSA (Heterogeneous System Architecture) stuff. This is AMD/ARM (and many friends)’s plan for the future, and it is pretty fucking exciting (in an obscure technical sort of way).

The best starting point I found is this year old whitepaper [PDF warning]. They’re using slightly odd terminology, the important bits are LCU = Latency Compute Unit = Conventional MIMD CPU Core, TCU = Throughput Compute Unit = Accelerator, typically SIMD-engine-ish like a GPU, HSAIL = HSA Intermediate Language = IR that can be compiled at install/run time to accelerator’s ISAs. The hardware-side implementation details are nowhere to be found, but there are a lot of seriously exciting model-affecting things detailed on the software side. The general model, with things broken into grid, work group, work item, wavefront is FAR more sane than most of the parallel schemes (I’m thinking specifically of the awful CUDA nomenclature). Internally, the exciting stuff includes requiring a limited sort of preemption on the accelerators, a relaxed consistency model across memory shared over a whole system (nice thread-like shared memory), an intermediate low level language/VM for portability, and assurances about barrier capability in the TCU. The actual objects are basically FAT ELFs with a complete copy of the program for the LCU, plus the HSAIL representation for the parts that can be shipped to TCUs. I’m pleased that there seems to be a clever run-time that does a bunch of platform enumeration and controls where parts run in a rule-automated-but-overrideable way.

I had some folks at SC tell me they’d try to get me a more implementation-focused whitepaper on the hardware side at AMD but they weren’t sure if/when details would be clear for distribution. On the software side, the details are in a published draft of the ISA/Model/Compiler Writer’s Guide that I browsed around in a bit and found very enlightening. The reference tool-chain seems to be mostly built on LLVM and OpenCL.

I have some other SC-related thoughts to share, but I want to get them a little bit more refined (and decide which are for public consumption) before I post.

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SC13

Posted on 2013-11-15 by pappp

I will be at SC’13 November 16-21 with the aggregate.org/University of Kentucky research exhibit again this year in booth 629. Media and impressions should appear somewhere in my ‘net presence during and after the conference, it is always a good show.
Edit:Pushing photos from the show floor into this album.

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chdk-ptp PKGBUILD

Posted on 2013-11-10 by pappp

In another episode of fixing things for the Cameras as Computing Systems class I’m taking, I made a PKGBUILD that apparently correctly builds and installs chdk-ptp on Archlinux systems. Chdk-ptp is a tethered-control application for Canon cameras running CHDK, that hooks a variety of custom extensions to the ptp protocol. Their build system is a little lackluster, is missing things like an install rule, and requires a helper script be installed to do some path munging before running the binary, but the documentation is good enough to sort it out, and the program itself seems to work. My package depends on iup-all-bin from the AUR which also provides the cd dependency (not marked in its provides array, though there isn’t an official package to conflict with). I tried to use the built-from-source AUR packages for cd (Seriously, who thought that was a good name for a piece of software?) and iup, but iup was giving me a hassle and the chdk-ptp documentation suggests the binary distribution will be less trouble anyway.

The PKGBUILD format has changed a bit since I was last making my own- I like most of the changes in terms of clarity and modularity, but it does require a bit of re-learning. It also means I have a couple of pet packages that probably need attention.

The build is a little janky so despite it passing through namcap with only one expected warning, I don’t want to put it in the AUR until I’ve tested it enough to be reasonably sure it works as intended. I expect I will get around to that eventually.

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Gigabit to The Home BoF Opening Presentation

Posted on 2013-11-01 by pappp

I gave the discussion-starting talk for this week’s CS departmental BoF session. The topic this week was “Unlimited Internet bandwidth – Would it be a game changer or no big deal?” My opening talk was just to get people up to date on the current events to kick off a discussion, though it is very similar to asking “What will we do with the internet” in the early ’80s, and thus rather difficult to suggest up plausible cases that aren’t “The same thing but faster.”

Callout:

Gigabit to the home is rapidly becoming a reality. Programmable hundred gigabit networks are already being constructed. Cellular networks are improving so fast that people are dumping their wired connections in favor of wireless. In short, networks are becoming so fast that one can begin to imagine a world where bandwidth is essentially unlimited.

But how would the world change if we had (essentially) unlimited bandwidth to everywhere? Would it change anything? Don’t most apps already have all the bandwidth they need? Aren’t networks already fast enough to support “the Cloud”? Have we already max’d out on bandwidth? Are there any super-cool apps that could still be enabled by even faster networks? If so, what are they? Will they be truly radical, or just an incremental improvement?

Come and find out at our next CS Bof, Friday, Nov 1 at 3pm when we will debate whether there are apps that will benefit from even faster network speeds. If there was unlimited bandwidth, what new apps could *you* see emerging? Join us Friday to dream about the possibilities and give your opinion.

Slides , Notes

In a related note, I’ve made slides for several presentations recently in Beamer, including this one, and I’m pretty convinced I’m never voluntarily using Powerpoint or any obstinate WYSIWYG slide system again. Beamer is a superior tool for the job for every kind of presentation using slides I’ve ever run into.

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As a quick “look at me being a good citizen,” a “class projects sometimes do have positive externalities,” and so that I have a convenient pointer/local copy, I just touched up the script for building a GCC 4.5 toolchain suitable … Continue reading →

Posted on 2013-10-01 by pappp | Leave a comment

Udisks2 Misfeature Fix

Posted on 2013-08-25 by pappp

Apparently David Zeuthen committed a patch back in February (appears in udisks2 >= 2.0.91, afik) that lets you single-point (or selectively) switch Udisks2 back to the nice, sane, predictable “Removable drives mount to /media” behavior instead of the asinine “Drives are owned by some user who happens to be logged in at a local session at the time they are plugged, mounted to /run/media/$USER/$LABEL, and ACL’d to that user” nonsense that has been a near-constant source of inconvenience lately. I’m surprised it took me this long to find it.

Following these instructions, all you have to do is create a Udev rule (ie. /etc/udev/rules.d/99-correct-media-mount-point.rules) with the line ENV{ID_FS_USAGE}=="filesystem|other|crypto", ENV{UDISKS_FILESYSTEM_SHARED}="1", and storage mounts to /media/$LABEL (You may want to leave out crypto, it actually makes sense for encrypted volumes to be obscured from other users like that) with no funky ACLs by default.

No more tedious user,noauto,nofail fstab entries on all my machines, for all my frequently-used discs to prevent that behavior! Hurrah!

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N109 Thinkpad AC Adapters

Posted on 2013-06-16 by pappp

N109-6

Since I’ve been documenting failure modes in electronics, another tale of electronic woe regarding N109 type knockoff Lenovo 90W AC adapters. I have a couple T series ThinkPads, which conveniently all use the same 20V 90W supplies with the same connector. I noticed that the stress relief on one of my AC adapters was wearing, so, having had a streak of good luck buying various direct-from-China products, I bought a knockoff replacement adapter that way.
I would suggest that you don’t want do that.
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I got into another discussion about Linux init systems. Since I still get a lot of hits about that, I figure I should put a link, as the long two-part post is a reasonably clean and complete explanation of my … Continue reading →

Posted on 2013-05-29 by pappp | Leave a comment