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Spencer
Advanced Newbie
Joined: 06 Nov 2005
Posts: 99
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 Posted: 24 Oct 2008 12:02:54 pm Post subject: |
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I know there are some Linux users around here that may be able to help. I've got a real challenge for you, this is quite a tricky problem.
I ported Linux 2.6.24 to a simple PowerPC board (4 MB RAM, 8 MB flash) and wrote the requisite device drivers to bring up the USB and serial ports. It works great, until I enable TCP/IP in the kernel. At which point the performance drops by at least a factor of 10x. Simple programs like "ls" take a very long time to execute.
TCP/IP works. I enabled the ethernet over USB driver, and a small webserver can serve pages to a host Windows PC. However, the system performance should not have dropped so much!
The system does not have swap, so if it were out of RAM I would hear about it (and programs or the kernel would simply stop working). Even so, /proc/meminfo claims there is still 500 KB free. The only options for networking enabled are CONFIG_NET (Networking) and CONFIG_INET (TCP/IP v4).
Is there any sort of configuration for the kernel that could cause this? Busybox's top can display CPU times, it claims 96% is idle (with 4% used by top).
Any tips for perhaps setting up a system profiler to determine what's going wrong in the kernel? I haven't gotten newer releases of the kernel to work yet, but I don't believe the network components I'm using have changed much since 2.6.24.
Thanks for the help! |
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Spencer
Advanced Newbie
Joined: 06 Nov 2005
Posts: 99
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| Posted: 24 Oct 2008 06:32:32 pm Post subject: |
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Today was the first full day I got to devote to this and I may have found an answer.
Including TCP/IP in the kernel bumped the RAM usage up 250 more KB. I didn't mention the JFFS2 filesystem earlier, but it ended up being the issue. The high RAM usage most likely triggered the filesystem to use a less effective, but more memory efficient, decompression routine.
This is one of those Linux issues that could've been helped by better documentation. Part of the problem was it was unclear that JFFS2 used compression by default. I guess it's time to submit a patch to the JFFS2 docs! (and perhaps add a printk for when it reverts to a slower decompression routine) |
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