On Saturday 26 January 2008 02:03, Asbjørn Sannes wrote: > Asbjørn Sannes wrote: > > Nick Piggin wrote: > >> 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. > > > > I'm going to run some tests without limiting the memory to 80 megabytes > > (so that it is 2 gigabyte) and see how much it varies then, but iff I > > recall correctly it did not vary much. I'll reply to this e-mail with > > the results. > > 5 runs gives me: > real 5m58.626s > real 5m57.280s > real 5m56.584s > real 5m57.565s > real 5m56.613s > > Should I test with tmpfs aswell?
I wouldn't worry about it. It seems like it might be due to page reclaim (fs / IO can't be ruled out completely though). Hmm, I haven't been following reclaim so closely lately; you say it started going bad around 2.6.22? It may be lumpy reclaim patches? -- 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/
