Category Archives: Computers

Miscellanious Computing

Default ext3 mode changing in 2.6.30 (updated)

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Here’s something for Linux users to be cognisant of – the default mount option for ext3’s journaling is going to changing from “data=ordered” (i.e. data is committed to disk prior to its metadata) to “data=writeback” (i.e. file metadata may be committed to disk before the file data is). This may be down to Ted Ts’o’s fixes for ext3 fsync() latency in that mode which spawned a long thread on the ext4 list.

Update: apparently Ted floated the idea at the 2009 Linux Storage & Filesystems Workshop, in his session “fsync(), rename(), barriers” – the LWN article notes it made people nervous, saying:

This idea was received with a fair amount of discomfort. The data=writeback mode brings back problems that were fixed by data=ordered; after a crash, a file which was being written could turn up with completely unrelated data in it. It could be somebody else’s sensitive data. Even if it’s boring data, the problem looks an awful lot like file corruption to many users. It seems like a step backward and a change which is hard to justify for a filesystem which is headed toward maintenance mode. So it would be surprising to see this change made.

It was later followed by the post script: “[After writing the above, your editor noticed that Linus had just merged a change to make data=writeback the default for ext3 in 2.6.30. Your editor, it seems, is easily surprised.]“.

Given the massive filesystem thread I guess this is going to make for more interesting times on LKML.. ;-/

Update 2: Forgot to mention too that the relatime option will be the default in 2.6.30, so by default the access time of a file will no longer be updated for every read.

Donna’s painting clearance sale :-)

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My wife Donna has been painting and sculpting for years (not to mention writing and composing), and has sold almost 100 of her originals worldwide so far. Problem is that she paints far faster than people buy them so she’s doing a bit of a clearance sale on eBay at the moment as we’ve run out of room in the house! 🙂

The 13 pieces are both figurative and abstract pieces of autistic art; some in oils, some in acrylics and some in mixed media. The starting bids on these pieces are just $10-$15 and have 4 days to go. You too can be a budget collector of outsider art!

RIP SGI – now owned by Rackable Systems

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Silicon Graphics (SGI) is no more, they filed for Chapter 11 bankruptcy protection on April 1st and have just been bought by Rackable Systems. I don’t think this is an elaborate April Fool (and if it was I think the SEC might have a thing or two to say about it). Both Rackable and SGI have identical press releases (Rackable PR – SGI PR) on the transaction for a mere US$25 million.

FREMONT, CA and SUNNYVALE, CA., April 1, 2009 – Rackable Systems, Inc. (NASDAQ:RACK), a leading provider of servers and storage products for medium to large-scale data centers, today announced its agreement to acquire substantially all the assets of Silicon Graphics, Inc. (SGI) (NASDAQ: SGIC) for approximately $25 million in cash, subject to adjustment in certain circumstances, plus the assumption of certain liabilities associated with the acquired assets.
[…]

Rackable has signed an Asset Purchase Agreement to acquire substantially all the assets of SGI, and to assume certain liabilities relating to the assets, pursuant to Chapter 11 of the U.S. Bankruptcy Code, under which SGI filed its petition in New York on April 1, 2009

I guess it’s better than SGI going under completely, but there’s going to be a number of customers now rather worried about their investments..

The snooping dragon: social-malware surveillance of the Tibetan movement

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Shishir Nagaraja of the University of Illinois at Urbana-Champaign and Ross Anderson of Cambridge University have published a very interesting paper called “The snooping dragon: social-malware surveillance of the Tibetan movement” (abstract, full report) on how agents of the Chinese government managed to infiltrate the computer network of the Dalai Lama’s organisation through ingenious social engineering and gain access to intelligence information that could lead to peoples arrest and possible execution.

It’s a very interesting report and points out that the techniques used are within the reach of motivated individuals as well as government intelligence agencies and ponders how much less well known organisations can cope with such attacks; it also lends weight to the sage advice offered in Ross Andersons “Security Engineering” book. Both are well worth a read, even for those of us whose network security is not a literal matter of life or death.

Sensible talk on patents from ZDNet

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Like many western nations that built up their industries under protective laws and now demand that developing countries remove restrictions that they relied on we see Microsoft doing much the same with Tom Tom, as ZDNet points out when discussing why Microsoft are eager to avoid talking about the details of their patent case..

The TomTom claims cover such things as a multitasking computer on which you can run programs, in a car. A wireless Internet-connected computer, in a car. And how to create long file names in the MS-DOS filing system–a fix introduced in Windows 95 because MS-DOS is a direct descendent of 1974’s vintage 8-bit CP/M operating system. A direct descendant? More a bastard child: MS-DOS helped itself freely to many of CP/M’s design concepts, in some detail. But those were the days when Bill Gates could say that software patents had the potential to put the industry at “a complete standstill” and with good reason. If the sort of protection Microsoft now claims for itself had been available to CP/M then, Microsoft would never have created its monopoly, nor amassed a fraction of its power.

Hopefully Tom Tom now being a member of the Open Invention Network will give Microsoft pause for thought. As regards how the system currently works, I cannot put it better than how ZDNet sum it up:

The patent system is not just broken, it is poisonous. It works by fear, using the civil courts as cudgels in the hands of bullies.

Sadly I suspect it’s unlikely to change in the near future.. 🙁

iiNet pulls out of Australian censorship pilot

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I know iiNet always said they were only going to participate to show that this couldn’t work, but now they’ve decided it’s not even worth doing that given recent developments..

“It became increasingly clear that the trial was not simply about restricting child pornography or other such illegal material, but a much wider range of issues including what the Government simply describes as ‘unwanted material’ without an explanation of what that includes.” “Everyone is repulsed by, and opposed to, child pornography but this trial and policy is not the solution or even about that.”

Hooray..

This is completely nuts

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Excuse me – but can someone unbreak Australia ? (…and no, that’s not an invitation to the Liberal/National party, you introduced this in the first place and would just screw it up even more).

On 16 March 2009, the Australian Communications and Media Authority added Wikileaks to their blacklist, and threatened anyone linking to the site with $AU11,000-a-day fines. The site will be blocked for all Australians if the mandatory internet filtering censorship scheme is implemented as planned.

Yada yada yada..

You’ve got to wonder what sort of blacklist has the website of a Queensland dentist on it – I know people are afraid of dentists but this is taking it a bit far..

Apparently you can get fined $11,000 a day for linking to a page that you’re not allowed to know is banned, it makes the EU’s secret ban on tennis racquets (ok, blunt instruments) on planes seem almost tame..

For useful insights see Brendan Scott’s blog on the topic, and this one on the leaking…

Comparing Fortran Compilers

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I’m just testing out the Fortran 90 compilers on our AMD quad core cluster Tango based on some code that Joe Landman wrote as a test case in January 2008, using the same input file as him. The compilers I’m using are GCC 4.3.3, Intel 11.0.81 and PGI 8.0-3.

For the unoptimised (-O0) version I get:

  • GCC: 1.884s
  • Intel: 3.891s
  • PGI: 1.170s

For basic optimisation (-O) I get:

  • GCC: 1.617s
  • Intel: 3.515s
  • PGI: 0.954s

Cranking up the optimisation to -O2 sees no change:

  • GCC: 1.610s
  • Intel: 3.514s
  • PGI: 0.954s

Now we add compiler specific flags:

  • GCC (-march=amdfam10 -O3): 0.956s
  • Intel (-fast): 3.507s
  • PGI (-fast -tp shanghai-64): 0.997s

That got me wondering which had the greater impact, -O3 or the -march=amdfam10 and the result was surprising:

  • GCC (-O3): 1.611s
  • GCC (-march=amdfam10 -O0): 1.238s

So that’s pretty conclusive, just enabling the AMD k10h CPU (i.e. Barcelona/Shanghai processors) with no optimisations gives a better speedup than the highest level of optimisation! Of course it’s better with both, as you can see from the previous set of results.

I’m *really* impressed by GCC’s performance there, as well as the PGI unoptimised speed, and disappointed by the Intel compilers general lack of performance. I suspect Intels answer would be (not unreasonably) that they don’t necessarily target performance for their competitors CPUs.