monline

I've set up LTSP-5 with Xubuntu 6.10 and found that at some point during the boot process of the thin clients (in the "Setting up LTSP client..." phase) it seemed to "stall" for a very long time (several minutes!). My thin clients are very "thin" indeed (we use old Compaq Evo T20 clients with a ~300MHz Geode GX1 CPU and 64MB of RAM), which might be the reason for the slow boot process. However I did not want to accept it as a fact since with LTSP-4.x I did not experience anything like this.

I digged into the issue and came up with the following result: each invocation of the preseed() function within the ltsp-client-setup script took around 10-12 seconds on my thin clients. The fact is that the execution of debconf-communicate has a fairly large overhead (at least on my thin clients), but the processing of its input commands has a quite acceptable speed. Fortunately debconf-communicate can accept multiple commands on its input, separated by newlines. My first test was to merge the two debconf-communicate calls within preseed() into one call, like this:

Original:
Merged:

This took down the execution time of a preceed() call from 10-12 secs to 5-6secs! This seemed very promising so I worked on it a bit further. I've modified the preseed() function not to execute debconf-communicate on each call, but only "collect" the parameters in a variable, and added to the end of configure_x() to pipe all the commands in one batch to debconf-communicate. The result is that instead of several minutes, now configure_x() runs in ~30 seconds on my clients.

As already mentioned, I use Xubuntu 6.10 where the latest version of ltsp-server is 0.124. In the ltsp-client-setup script in this LTSP version there're in "worst" case 19 calls to the preseed() function and each call has 2 debconf-communicate calls (a preseed() call took approx. 10s on my clients). These all together can took 6.5 minutes on my site, but with my patch it takes only 6 seconds! The execution time of debconf-communicate remained almost unchanged regardless of how many commands I piped into it. More than 60 times speedup ... not bad.

Of course this is only true on my slow Evo T20 thin clients. My modifications would not have such a huge impact on faster thin clients. I've attached both the full, modified version of ltsp-client-setup and a patch, where you can spot the modifications a lot more easily.

Attachment	Size
ltsp-client-setup-0.124.new	11.22 KB
ltsp-client-setup-0.124.patch	6.02 KB