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? -- Asbjorn Sannes -- 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/
