On Tue, Jan 25, 2011 at 10:17:41AM +0100, Edgar E. Iglesias wrote: > On Mon, Jan 24, 2011 at 04:28:48PM -0600, Anthony Liguori wrote: > > On 01/24/2011 03:00 PM, Anthony Liguori wrote: > > > Leave the disable options for now to help with testing but these will be > > > removed > > > once we're confident in the thread implementations. > > > > > > Disabled code bit rots. These have been in tree long enough that we need > > > to > > > either commit to making them work or just remove them entirely. > > > > > > > I/O thread disables icount apparently. > > > > I'm not really sure why. Marcelo, do you know the reason > > qemu_calculate_timeout returns a fixed value in the I/O thread > > regardless of icount? > > Hi, > > The following commit hopefully fixed that issue. > > commit 225d02cd1a34d5d87e8acefbf8e244a5d12f5f8c > Author: Edgar E. Iglesias <edgar.igles...@gmail.com> > Date: Sun Jan 23 04:44:51 2011 +0100 > > Avoid deadlock whith iothread and icount > > When using the iothread together with icount, make sure the > qemu_icount counter makes forward progress when the vcpu is > idle to avoid deadlocks. > > Signed-off-by: Edgar E. Iglesias <edgar.igles...@gmail.com> > > See http://lists.gnu.org/archive/html/qemu-devel/2011-01/msg01602.html > for more info. > > One more thing I didn't mention on the email-thread or on IRC is > that last time I checked, qemu with io-thread was performing > significantly slower than non io-thread builds. That was with > TCG emulation (not kvm). Somewhere between 5 - 10% slower, IIRC. > > Also, although -icount & iothread no longer deadlocks, icount > still sometimes performs incredibly slow with the io-thread (compared > to non-io-thread qemu). In particular when not using -icount auto but > a fixed ticks per insn values. Sometimes it's so slow I thought it > actually deadlocked, but no it was crawling :) I haven't had time > to look at it any closer but I hope to do soon. > > These issues should be fixable though, so I'm not arguing against > enabling it per default. Just mentioning what I've seen FYI..
Right, remember seeing 20% added overhead for network copy with TCG on the initial iothread merge. One can argue its due to the added overhead of locking/signalling between vcpu and iothread, where neither can run in parallel (while in kvm mode they can). But its just handwaving until detailed information is gathered on specific cases...
