* Nikola Ciprich (nikola.cipr...@linuxbox.cz) wrote: > Hi, > > I was doing some I/O tuning of our KVM host, and noticed some > strange behaviour. When I start some heavy I/O load on guest > (ie run some fio benchmark), loadavg value of the host jumps > to value about 65 and holds until load ends. sar reports similar > number of blocked tasks. I don't really understand those numbers, > because only active tasks are 4 qemu-kvm threads and few other sleeping > tasks (so none in R or D state). > is it possible to somehow find which tasks seem to be blocked? > or why is loadavg value so high? > the system is x86_64 quad core with 4GB RAM running centos 6 with 3.0.52-rc1 > kernel.
Recebt qemu split there io across multiple threads (as an alternative to AIO), so what you"ll see is each qemu will dynamically start a load of threads when is doing heavy IO, none of them will usr much cpu, but each will be blocking on io, and hence count as a 1 for the load. It does have some flags (which I forget) that let you limit the number of threads or flip to AIO. Other than getting a scary loadavg number, it doesn't seem to have any bad effecta. Dave -- -----Open up your eyes, open up your mind, open up your code ------- / Dr. David Alan Gilbert | Running GNU/Linux | Happy \ \ gro.gilbert @ treblig.org | | In Hex / \ _________________________|_____ http://www.treblig.org |_______/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
