On 11/07/2012 10:02 PM, Stefan Priebe wrote: > Hello again, > > I've noticed something really interesting. > > I get 5000 iops / VM for rand. 4k writes while assigning 4 cores on a > 2.5 Ghz Xeon. > > When i move this VM to another kvm host with 3.6Ghz i get 8000 iops > (still 8 cores) when i then LOWER the assigned cores from 8 to 4 i get > 14.500 iops. If i assign only 2 cores i get 16.000 iops... > > Why does less kvm cores mean more speed?
Totally going on a limb here, but might be related to the cache maybe? When you have more cores your threads may bounce around the cores and invalidate cache entries as they go by; will less cores you might end up with some sort of twisted, forced cpu affinity that allows you to take advantage of caching. But I don't know, really. I would be amazed if what I just wrote had an ounce of truth, and would be completely astonished if that was the cause for such a sudden increase on iops. -Joao > > Greets, > Stefan > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
