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[Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHR
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2) |
Date: |
Thu, 17 Feb 2011 09:27:43 +0100 |
User-agent: |
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On 02/17/2011 04:15 AM, Marcelo Tosatti wrote:
Yes, using qemu_icount_delta directly in tcg_wait_io_event timedwait
is explicit (partially the reason for confusion with my patch).
So the reasoning for the patch is:
With icount vm_timer timers expire on virtual CPU time. If a CPU halts,
you cannot expect passage of realtime to trigger vm_timers expiration.
But if a CPU is halted, all_cpu_threads_idle() will still be true even
if you signal the condition variable, and you'll be looping in the while
condition. That's why I say that
while (x) {
cond_timedwait (cond, mutex);
}
(i.e. without checking the return value of cond_timedwait, and without
polling something else upon return) is a broken idiom that can only work
around missing signals/broadcasts.
So instead vm_timer expiration is converted to realtime, and used as
halt timeout.
But vm_timer timers are only used by "-icount auto", which works in my
tests [*]. It is "-icount N" which is broken and unfortunately your
patch does not fix it. The CRIS image on qemu.org triggers the watchdog
(and if I eliminate the watchdog I see that the CPU is hung).
[*] Actually, it works but doesn't calibrate very well. It shows
25 bogomips, sometimes 50, compared to 250 without iothread.
Paolo
- [Qemu-devel] [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), (continued)
- [Qemu-devel] [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Marcelo Tosatti, 2011/02/15
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Jan Kiszka, 2011/02/16
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Paolo Bonzini, 2011/02/16
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Jan Kiszka, 2011/02/16
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Paolo Bonzini, 2011/02/16
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Jan Kiszka, 2011/02/16
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Paolo Bonzini, 2011/02/16
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Jan Kiszka, 2011/02/16
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Paolo Bonzini, 2011/02/16
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Marcelo Tosatti, 2011/02/16
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2),
Paolo Bonzini <=
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Paolo Bonzini, 2011/02/18
- [Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2), Jan Kiszka, 2011/02/17