Subject: Re: LFS on multi-processor systems
To: Brian de Alwis <firstname.lastname@example.org>
From: Zafer Aydogan <email@example.com>
Date: 09/19/2007 11:05:46
2007/9/19, Brian de Alwis <firstname.lastname@example.org>:
> I decided to try using LFS on an MP laptop [*]. This was on a kernel
> from 4.99.31. I used the defaults from sysinst of a 16k block size and
> 2k fragment size, and 1MB segment size.
Can you verify that hangs and panics disappear when booting an UP kernel ?
> I experienced pretty frequent hard hangs. I tried boosting kern.maxvnodes
> to 131072 and 262144, which overall seemed to lengthen the amount of time
> before a crash, but it would still periodically hang almost right away.
> I once got a "panic: lfs_rescount".
> The best way to cause a hang was to do a build.sh while running X and
I had no luck with MP aswell, but it's been a while.
I can confirm that at least on i386 with an UP kernel everything works
smooth, aslong you use default values (which is 8k/1k I think). I
usually skip the -A option.
> Watching vmstat -Wm, it looked like the various lfs inode pools were only
> increasing (I saw the numbers go up to 233k), with nothing being given
> back. This contrasted sharply with the ffs inode pools which always
> fluctuated around 4100. I had wondered if the hangs were related to
> this number hitting the maxvnodes, but then experienced 2 hard hangs
> in succession just shortly after a reboot, when the numbers were well
> below maxvnodes. And I'm now reinstalling onto an FFS filesystem, but
> seeing the same behaviour from the ffs inode pool as I saw with the
> lfs inode pools.
> It sure was nice having near-instantaneous fscks! :-)
Yes, it is.
I've recently set up a machine with normal "ffs" again and it is
extremely slow, compared to lfs, which means that I don't want to miss
But there is one thing I don't understand yet. It is not possible to
have a constant writing stream to disk, like during large ftp
transfers with lfs. It only writes in bursts every 5 - 10 seconds (see
iostat -w1), which causes the ftp connection speed to stall every 5-10
seconds (speed is going up and down). You won't probably notice it on
a dsl or dial up line, but if you transfer gigabytes through your LAN
with 100mbit/s you will see.
> Oh, I just saw from Blair's message that he used an 8k block size...
> Maybe I'll give that a try.
> [*] My FFS filesystem was recently hosed: my battery was running
> low, and the machine hung hard when I plugged in the adapter.
> On reboot, the filesystem was hosed, and fsck made many repairs.
> Subsequent fscks reported the filesystem as clean, but reinstalling
> the OS would result in panics about dup allocs.
> Brian de Alwis | Software Practices Lab | UBC | http://www.cs.ubc.ca/~bsd/
> "Amusement to an observing mind is study." - Benjamin Disraeli