On Friday 25 January 2008 22:32, Asbjorn Sannes wrote: > Hi, > > I am experiencing unpredictable results with the following test > without other processes running (exception is udev, I believe): > cd /usr/src/test > tar -jxf ../linux-2.6.22.12 > cp ../working-config linux-2.6.22.12/.config > cd linux-2.6.22.12 > make oldconfig > time make -j3 > /dev/null # This is what I note down as a "test" result > cd /usr/src ; umount /usr/src/test ; mkfs.ext3 /dev/cc/test > and then reboot > > The kernel is booted with the parameter mem=81920000 > > For 2.6.23.14 the results vary from (real time) 33m30.551s to 45m32.703s > (30 runs) > For 2.6.23.14 with nop i/o scheduler from 29m8.827s to 55m36.744s (24 runs) > For 2.6.22.14 also varied a lot.. but, lost results :( > For 2.6.20.21 only vary from 34m32.054s to 38m1.928s (10 runs) > > Any idea of what can cause this? I have tried to make the runs as equal > as possible, rebooting between each run.. i/o scheduler is cfq as default. > > sys and user time only varies a couple of seconds.. and the order of > when it is "fast" and when it is "slow" is completly random, but it > seems that the results are mostly concentrated around the mean.
Hmm, lots of things could cause it. With such big variations in elapsed time, and small variations on CPU time, I guess the fs/IO layers are the prime suspects, although it could also involve the VM if you are doing a fair amount of page reclaim. Can you boot with enough memory such that it never enters page reclaim? `grep scan /proc/vmstat` to check. Otherwise you could mount the working directory as tmpfs to eliminate IO. bisecting it down to a single patch would be really helpful if you can spare the time. Thanks, Nick -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
