On Friday 04 September 2009 11:08:51 am Andrew Theurer wrote: > Brian Jackson wrote: > > On Friday 04 September 2009 09:48:17 am Andrew Theurer wrote: > > <snip> > > > >>> Still not idle=poll, it may shave off 0.2%. > >> > >> Won't this affect SMT in a negative way? (OK, I am not running SMT now, > >> but eventually we will be) A long time ago, we tested P4's with HT, and > >> a polling idle in one thread always negatively impacted performance in > >> the sibling thread. > >> > >> FWIW, I did try idle=halt, and it was slightly worse. > >> > >> I did get a chance to try the latest qemu (master and next heads). I > >> have been running into a problem with virtIO stor driver for windows on > >> anything much newer than kvm-87. I compiled the driver from the new git > >> tree, installed OK, but still had the same error. Finally, I removed > >> the serial number feature in the virtio-blk in qemu, and I can now get > >> the driver to work in Windows. > > > > What were the symptoms you were seeing (i.e. define "a problem"). > > Device manager reports "a problem code 10" occurred, and the driver > cannot initialize. Yes! I was getting this after I moved from 0.10.6 to 0.11.0-rc1. Now I know how to fix it. Thank you. Thank you. > > Vadim Rozenfeld informed me: > > There is a sanity check in the code, which checks the I/O range and fails > > if is not equal to 40h. Resent virtio-blk devices have I/O range equal to > > 0x400 (serial number feature). So, out signed viostor driver will fail > > on the latest KVMs. This problem was fixed > > and committed to SVN some time ago. > > I assumed the fix was to the virtio windows driver, but I could not get > the driver I compiled from latest git to work either (only on > qemu-kvm-87). So, I just backed out the serial number feature in qemu, > and it worked. FWIW, the linux virtio-blk driver never had a problem. There have been very few changes to the viostor windows git repo since it was opened. Unless it was done before they were open sourced. In any case, it doesn't seem to be working with what's publicly available, so I think maybe there is something missing internal to external. > > >> So, not really any good news on performance with latest qemu builds. > >> Performance is slightly worse: > >> > >> qemu-kvm-87 > >> user nice system irq softirq guest idle iowait > >> 5.79 0.00 9.28 0.08 1.00 20.81 58.78 4.26 > >> total busy: 36.97 > >> > >> qemu-kvm-88-905-g6025b2d (master) > >> user nice system irq softirq guest idle iowait > >> 6.57 0.00 10.86 0.08 1.02 21.35 55.90 4.21 > >> total busy: 39.89 > >> > >> qemu-kvm-88-910-gbf8a05b (next) > >> user nice system irq softirq guest idle iowait > >> 6.60 0.00 10.91 0.09 1.03 21.35 55.71 4.31 > >> total busy: 39.98 > >> > >> diff of profiles, p1=qemu-kvm-87, p2=qemu-master > > > > <snip> > > > >> 18x more samples for gfn_to_memslot_unali*, 37x for > >> emulator_read_emula*, and more CPU time in guest mode. > >> > >> One other thing I decided to try was some cpu binding. I know this is > >> not practical for production, but I wanted to see if there's any benefit > >> at all. One reason was that a coworker here tried binding the qemu > >> thread for the vcpu and the qemu IO thread to the same cpu. On a > >> networking test, guest->local-host, throughput was up about 2x. > >> Obviously there was a nice effect of being on the same cache. I > >> wondered, even without full bore throughput tests, could we see any > >> benefit here. So, I bound each pair of VMs to a dedicated core. What I > >> saw was about a 6% improvement in performance. For a system which has > >> pretty incredible memory performance and is not that busy, I was > >> surprised that I got 6%. I am not advocating binding, but what I do > >> wonder: on 1-way VMs, if we keep all the qemu threads together on the > >> same CPU, but still allowing the scheduler to move them (all of them at > >> once) to different cpus over time, would we see the same benefit? > >> > >> One other thing: So far I have not been using preadv/pwritev. I assume > >> I need a more recent glibc (on 2.5 now) for qemu to take advantage of > >> this? > > > > Getting p(read|write)v working almost doubled my virtio-net throughput in > > a Linux guest. Not quite as much in Windows guests. Yes you need > > glibc-2.10. I think some distros might have backported it to 2.9. You > > will also need some support for it in your system includes. > > Thanks, I will try a newer glibc, or maybe just move to a newer Linux > installation which happens to have a newer glic. Fwiw... In Debian, I had to get glibc from the experimental tree. So some distros might not even have it. > > -Andrew > -- 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
