On 2011-02-23 13:40, Edgar E. Iglesias wrote: > On Wed, Feb 23, 2011 at 12:39:52PM +0100, Jan Kiszka wrote: >> On 2011-02-23 12:08, Edgar E. Iglesias wrote: >>> On Wed, Feb 23, 2011 at 11:25:54AM +0100, Paolo Bonzini wrote: >>>> On 02/23/2011 11:18 AM, Edgar E. Iglesias wrote: >>>>> Sorry, I don't know the code well enough to give any sensible feedback >>>>> on patch 2 - 4. I did test them with some of my guests and things seem >>>>> to be OK with them but quite a bit slower. >>>>> I saw around 10 - 20% slowdown with a cris guest and -icount 10. >>>>> >>>>> The slow down might be related to the issue with super slow icount >>>>> together >>>>> with iothread (adressed by Marcelos iothread timeout patch). >>>> >>>> No, this supersedes Marcelo's patch. 10-20% doesn't seem comparable to >>>> "looks like it deadlocked" anyway. Also, Jan has ideas on how to remove >>>> the synchronization overhead in the main loop for TCG+iothread. >>> >>> I see. I tried booting two of my MIPS and CRIS linux guests with iothread >>> and -icount 4. Without your patch, the boot crawls super slow. Your patch >>> gives a huge improvement. This was the "deadlock" scenario which I >>> mentioned in previous emails. >>> >>> Just to clarify the previous test where I saw slowdown with your patch: >>> A CRIS setup that has a CRIS and basically only two peripherals, >>> a timer block and a device (X) that computes stuff but delays the results >>> with a virtual timer. The guest CPU is 99% of the time just >>> busy-waiting for device X to get ready. >>> >>> This latter test runs in 3.7s with icount 4 and without iothread, >>> with or without your patch. >>> >>> With icount 4 and iothread it runs in ~1m5s without your patch and >>> ~1m20s with your patch. That was the 20% slowdown I mentioned earlier. >>> >>> Don't know if that info helps... >> >> You should try to trace the event flow in qemu, either via strace, via >> the built-in tracer (which likely requires a bit more tracepoints), or >> via a system-level tracer (ftrace / kernelshark). > > Thanks, I'll see if I can get some time to run this more carefully during > some weekend. > >> >> Did my patches contribute a bit to overhead reduction? They specifically >> target the costly vcpu/iothread switches in TCG mode (caused by TCGs >> excessive lock-holding times). > > Do you have a tree for quick access to your patches? (couldnt find them > on my inbox).
http://thread.gmane.org/gmane.comp.emulators.qemu/93765 (looks like I failed to CC you) and they are also part of git://git.kiszka.org/qemu-kvm.git queues/kvm-upstream > > I could give them a quick go and post results. > > Cheers Thanks, Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux
