Software and hardware annotations 2010 May

This document contains only my personal opinions and calls of judgement, and where any comment is made as to the quality of anybody's work, the comment is an opinion, in my judgement.

[file this blog page at: digg Technorati]

100529 Sat Laptop battery capacity decaying

As previously noted my laptop battery capacity is decaying quickly it looks like that the speed of capacity decay has increased over time, as these are the days in which capacity was reduced:

090728    Last full capacity : 7300 mAh, 93.59% of design capacity
091101    Last full capacity : 7028 mAh, 90.10% of design capacity
100129    Last full capacity : 6595 mAh, 84.55% of design capacity
100212    Last full capacity : 6234 mAh, 79.92% of design capacity
100424    Last full capacity : 5787 mAh, 74.19% of design capacity
100426    Last full capacity : 4630 mAh, 59.36% of design capacity
100428    Last full capacity : 4065 mAh, 52.12% of design capacity
100519    Last full capacity : 3252 mAh, 41.69% of design capacity
100527    Last full capacity : 2871 mAh, 36.81% of design capacity

The battery was purchased in December 2008, so it decayed to half capacity in just over a year. The collapse since the end of April 2010 is partially due to my travelling a bit more in that period, and thus the battery was fully discharged more often and thus recharged more frequently.

Since the available capacity has been less than half of the original one I have to recharge the battery twice as often anyhow, and of course this increases the speed at which capacity is lost.

One way to make batteries keep their capacity longer is to remove them when the laptop is connected to a wall socket, but my laptop occasionally flakes out when I remove the battery while it is running. The reason seems to be that the logic that detects whether the battery is present or not is buggy and sometimes acts as if the battery has not been removed (the battery light on the front stays on), detects no power is coming from the battery, and then shutdownss the laptop, 10s-20s after wall socket power alone has kept the laptop running. In one particularly weird case I powered up the laptop without the battery, it started booting and then powered itself off after a while.

100520 Thu Anisotropic behaviour with many extents

From the often entertaining but also useful XFS mailing list an interesting point:

> We've got a couple of rather large files, and with a cold cache,
> reading the first 4K bytes of the file (e.g., just running
> "head --bytes 4096" on it) takes ages, up to several minutes,
> sometimes triggering the hang check timer.
> I wonder if XFS reads the whole extent information into RAM when the
> file is opened.  Is this the case, at least on 2.6.26?  Has this
> changed in later versions, perhaps?

Yes, XFS always reads in the extent map, and no this hasn't changed