Monthly Archives: March 2013

OMG! I just pushed the wrong branch…

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Today I’ve done a lot of rebasing with a series of patches that I needed to push to the master branch of some project. The patches originated from a branch named injector and I prepared the merge in another branch named injector-merge. When it came time to merge my branch back into master I should have written :

git merge injector-merge

But instead I wrote :

git merge injector

Damned auto completion ! Huh… That wouldn’t be so bad if only I hadn’t pushed that to upstream too… So I had to get rid of my master branch and replace it upstream as quickly as possible before anybody could clone or pull from it. By chance this is a fairly new project and I guess nobody cloned or pulled in such a short amount of time (this whole thing lasted no more than one minute or so). So I moved my master branch and replaced it with the injector-merge branch and pushed-force everything.

git checkout master
git branch -m oldmaster
git branch -m injector-merge master
git log

Hum… Everything seems to be in order! Now push it back! 

git push -f origin master

No complaining so far? Right! Well from now on I will call the merge branches merge-* instead of *-merge.

Get rid of that Non-Breaking space

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The non-breaking space is a variant of the space character which as the name suggests prevents automatic line breaking when using a space character. Another common use of it is to avoid collapsing of white-spaces in formats such as TeX or HTML. There are also some others specific typographic uses but nevermind.

From my point of view this character is a real pain, a annoying remain of a former era when the only editor you had was plain-text and which is now just good at invisibly polluting your work so that no compiler, interpreter or any other ASCII oriented tool would accept it anymore. For ASCII is not dead, it’s 7-bit, it’s common, it’s the neutral zone of all character set and No-Break Space shall not interfere therefore it must be eradicated from the very surface of earth or at least from my own keyboards.
There are several options to do that under Xorg. The first one would be to use the setxkbmap command to specify the nbsp:none option for your keyboard.
setxkbmap -option "nbsp:none"

However this won’t work as you might expect it especially when you have multiple keyboards with different layouts. So another solution would be to specify XkbOption directly within the Xorg configuration file, one for each input device. But this won’t work neither if you use a Bépo layout as this option will simply disable the use of underscore (AltGr Space). So the final solution is based on xmodmap to modify the list of keysyms assigned to the space keycode (0x41). You may just add the following line to ~/.xmodmap and ensure that the file is loaded when your session starts with xmodmap ~/.xmodmap.

keycode 65 = space space space space underscore underscore space space

Intel NIC connection problem

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PCIe ASPM is an hardware power management protocol for PCI express devices. It allows a far better power management than what can be done with software power management at the price of an increased latency to the device. However some hardware don’t advertise it properly. And this was in fact the origin of the power regression case of 2.6.38 which was later fixed in 3.3.

It may also cause some Intel NIC (such as e1000e) to fall asleep unintentionally. So if you have an Intel NIC on Linux and it even fails to acquire an IPv4 address then you might try to add this option to your kernel command line : pcie_aspm=off. On Debian you can add this option to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub and issue an update-grub.

You may also want to change the link-state of one specific device to L0/L1 at runtime. For this I’ll point you there : http://wireless.kernel.org/en/users/Documentation/ASPM.

Raspberry Pi Ethernet speed

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I’ve been a long time user of IPv6 tunnels from SixXS to provide an access to the IPv6 Internet behind my ISP. These tunnels also allow me to use static IP addresses for my home servers along with static AAAA records and this is cool !

Currently I use several Debian GNU/Linux based soft-routers with two (100 and 1000) Ethernet ports. These are often running on old recycled laptops which consumes around 40 Watts of power at peak level. Next to that the ARM Raspberry Pi platform consumes around 3 Watts of power (though I still have to measure it by myself). So I thought about replacing all my home-routers with those.

However the Raspberry Pi model B uses a SMSC LAN951x chip which includes the USB 2.0 Hub and an 10/100 Ethernet controller on top of it (which is known as smsc95xx in the Linux kernel). My  main concern was that it would not be fast enough to support the IPv6 tunnel at its peak bandwidth of 60Mbps (that is 30Mbps downstream/upstream).

I already use one RPi as an experimental home-router here. Our Internet bandwidth is a bit slow (12Mbps) so the USB-Ethernet  shouldn’t be a problem. I’ve conducted quick tests with IPerf and as you can see the results are pretty good as long as it doesn’t involve I/O on the RPi.

------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
[  4] local 10.0.0.1 port 5001 connected with 10.0.0.3 port 37373
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.1 sec   114 MBytes  94.4 Mbits/sec
[  5] local 10.0.0.1 port 5001 connected with 10.0.0.3 port 37376
[  5]  0.0-10.1 sec   114 MBytes  94.5 Mbits/sec
[  4] local 10.0.0.1 port 5001 connected with 10.0.0.3 port 37377
[  4]  0.0-10.1 sec   114 MBytes  94.6 Mbits/sec
[  5] local 10.0.0.1 port 5001 connected with 10.0.0.3 port 37378
[  5]  0.0-10.1 sec   114 MBytes  94.5 Mbits/sec