On Mon, 2015-08-24 at 13:04 -0400, Tejun Heo wrote: > Hello, Austin. > > On Mon, Aug 24, 2015 at 11:47:02AM -0400, Austin S Hemmelgarn wrote: > > >Just to learn more, what sort of hypervisor support threads are we > > >talking about? They would have to consume considerable amount of cpu > > >cycles for problems like this to be relevant and be dynamic in numbers > > >in a way which letting them competing against vcpus makes sense. Do > > >IO helpers meet these criteria? > > > > > Depending on the configuration, yes they can. VirtualBox has some rather > > CPU intensive threads that aren't vCPU threads (their emulated APIC thread > > immediately comes to mind), and so does QEMU depending on the emulated > > And the number of those threads fluctuate widely and dynamically? > > > hardware configuration (it gets more noticeable when the disk images are > > stored on a SAN and served through iSCSI, NBD, FCoE, or ATAoE, which is > > pretty typical usage for large virtualization deployments). I've seen cases > > first hand where the vCPU's can make no reasonable progress because they are > > constantly getting crowded out by other threads. Hm. Serious CPU starvation would seem to require quite a few hungry threads, but even a few IO threads with kick butt hardware under them could easily tilt fairness heavily in favor of VPUs generating IO. > That alone doesn't require hierarchical resource distribution tho. > Setting nice levels reasonably is likely to alleviate most of the > problem. Unless the CPU controller is in use. -Mike -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
