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[Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread
From: |
Edgar E. Iglesias |
Subject: |
[Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread |
Date: |
Wed, 23 Feb 2011 13:40:04 +0100 |
User-agent: |
Mutt/1.5.20 (2009-06-14) |
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).
I could give them a quick go and post results.
Cheers
- [Qemu-devel] [PATCH 0/4] Improve -icount, fix it with iothread, Paolo Bonzini, 2011/02/21
- [Qemu-devel] [PATCH 1/4] do not use qemu_icount_delta in the !use_icount case, Paolo Bonzini, 2011/02/21
- [Qemu-devel] [PATCH 3/4] rewrite accounting of wait time to the vm_clock, Paolo Bonzini, 2011/02/21
- [Qemu-devel] [PATCH 4/4] inline qemu_icount_delta, Paolo Bonzini, 2011/02/21
- [Qemu-devel] [PATCH 2/4] qemu_next_deadline should not consider host-time timers, Paolo Bonzini, 2011/02/21
- [Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread, Edgar E. Iglesias, 2011/02/23
- [Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread, Paolo Bonzini, 2011/02/23
- [Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread, Edgar E. Iglesias, 2011/02/23
- [Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread, Jan Kiszka, 2011/02/23
- [Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread,
Edgar E. Iglesias <=
- [Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread, Jan Kiszka, 2011/02/23
- [Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread, Paolo Bonzini, 2011/02/25
- [Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread, Paolo Bonzini, 2011/02/23
- [Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread, Edgar E. Iglesias, 2011/02/23
- [Qemu-devel] Re: [PATCH 0/4] Improve -icount, fix it with iothread, Paolo Bonzini, 2011/02/23