On Mon, Jul 6, 2009 at 8:28 AM, Michael Tokarev<mjt@xxxxxxxxxx> wrote: > Javier Guerra wrote: >> it also bothers me because when i have a couple of moderately >> disk-heavy VMs, the load average numbers skyrockets. that's because >> each blocked thread counts as 1 on this figure, even if they're all >> waiting on the same device. > > And how having large LA is bad? I mean, LA by itself is not an > indicator of bad or good performance, don't you think? it's not a real problem, of course; but it's a nuisance because some reporting tools (zabbix/nessus) use this figure to raise alarms, meaning i have to adjust it. also, even a single-threaded high-IO process on a guest fires a lot of IO threads on the host, and other not-so-aggressive VMs suffer. definitely using deadline scheduler on the host reduces the impact. (down to zero? i don't think so, but it's certainly manageable) >> on my own (quick) tests, changing the elevator on the guest has very >> little effect on performance; but does affect the host CPU >> utilization. using drbd on the guest while testing with bonnie++ >> increased host CPU by around 20% for each VM > > Increased compared what with what? Also, which virtual disk format > did you use? sorry, i had a typo there, i meant: using cfq vs. noop on the guest (running bonnie++, no drbd anywhere) produced around 20% more CPU load on the host, with no measurable performance advantage. -- Javier -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
