On Sun, Apr 20, 2008 at 02:16:52PM +0300, Avi Kivity wrote: > >The iperf numbers are pretty good. Performance of UP guests increase > >slightly but SMP > >is quite significant. > > I expect you're seeing contention induced by memcpy()s and inefficient > emulation. With the dma api, I expect the benefit will drop.
You still have to memcpy() with the dma api. Even with vringfd the kernel->user copy has to be performed under the global mutex protection, difference being that several packets can be copied per-syscall instead of only one. > >Note that workloads with multiple busy devices (such as databases, web > >servers) should > >be the real winners. > > > >What is the feeling on this? Its not _that_ intrusive and can be easily > >NOP'ed out for > >QEMU. > > > > > > I think many parts are missing (or maybe, I missed them). You need to > lock the qemu internals (there are many read-mostly qemu caches > scattered around the code), lock against hotplug, etc. Yes, there are some parts missing, such as the bh list and hotplug as you mention. > For pure cpu emulation, there is a ton of work to be done: protecting > the translator as well as making the translated code smp safe. I now believe there is a lot of work (which was not clear before). Not particularly interested in getting real emulation to be multithreaded. Anyways, the lack of multithreading in qemu emulation should not be a blocker for these patches to get in, since these are infrastructural changes. > I think that QemuDevice makes sense, and that we want this long term, > but that we first need to improve efficiency (which reduces cpu > utilization _and_ improves scalability) rather than look at scalability > alone (which is much harder in addition to the drawback of not reducing > cpu utilization). Will complete the QEMUDevice+splitlock patchset, keep it uptodated, and test it under a wider variety of workloads. Thanks. ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
