On 07/30/2014 06:12 AM, Chris Friesen wrote: > Hi, > > I've got an issue where we're hitting major performance penalties while doing live migration, and it seems like it might > be due to page faults triggering hypervisor exits, and then we get stuck waiting for the iothread lock which is held by > the qemu dirty page scanning code. I am afraid that using dirty-bit instead of write-protection may cause the case even more worse for iothread-lock because we need to walk whole sptes to get dirty-set pages, however currently we only need to walk the page set in the bitmap. > > Accordingly, I'm trying to figure out the actual mechanism whereby dirty pages are tracked in qemu/kvm. I've got an Ivy Bridge CPU, a 3.4 kernel on the host, and qemu 1.4. > > Looking at the qemu code, it seems to be calling down into kvm to get the dirty page information. > > Looking at kvm, most of what I read seems to be doing the usual "mark it read-only and then when we take a page fault mark it as dirty" trick. > > However, I read something about Intel EPT having hardware support for tracking dirty pages. It seems like this might avoid the need for a page fault, but might only be available on Haswell or later CPUs--is that correct? Is it supported in kvm? If so, when was support added? Actually, i have implemented the prototype long time ago, maybe it's the time to benchmark it and post it out. -- 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
