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[Qemu-devel] Re: MIPS, io-thread, icount and wfi
From: |
Edgar E. Iglesias |
Subject: |
[Qemu-devel] Re: MIPS, io-thread, icount and wfi |
Date: |
Tue, 18 Jan 2011 01:19:50 +0100 |
User-agent: |
Mutt/1.5.20 (2009-06-14) |
On Mon, Jan 17, 2011 at 11:03:08AM +0100, Edgar E. Iglesias wrote:
> Hi,
>
> I'm running an io-thread enabled qemu-system-mipsel with icount.
> When the guest (linux) goes to sleep through the wait insn (waiting
> to be woken up by future timer interrupts), the thing deadlocks.
>
> IIUC, this is because vm timers are driven by icount, but the CPU is
> halted so icount makes no progress and time stands still.
>
> I've locally disabled vcpu halting when icount is enabled, that
> works around my problem but of course makes qemu consume 100% host cpu.
>
> I don't know why I only see this problem with io-thread builds?
> Could be related timing and luck.
>
> Would be interesting to know if someone has any info on how this was
> intended to work (if it was)? And if there are ideas for better
> workarounds or fixes that don't disable vcpu halting entirely.
Hi,
I've found the problem. For some reason io-thread builds use a
static timeout for wait loops. The entire chunk of code that
makes sure qemu_icount makes forward progress when the CPU's
are idle has been ifdef'ed away...
This fixes the problem for me, hopefully without affecting
io-thread runs without icount.
commit 0f4f3a919952500b487b438c5520f07a1c6be35b
Author: Edgar E. Iglesias <address@hidden>
Date: Tue Jan 18 01:01:57 2011 +0100
qemu-timer: Fix timeout calc for io-thread with icount
Make sure we always make forward progress with qemu_icount to
avoid deadlocks. For io-thread, use the static 1000 timeout
only if icount is disabled.
Signed-off-by: Edgar E. Iglesias <address@hidden>
diff --git a/qemu-timer.c b/qemu-timer.c
index 95814af..db1ec49 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -110,7 +110,6 @@ static int64_t cpu_get_clock(void)
}
}
-#ifndef CONFIG_IOTHREAD
static int64_t qemu_icount_delta(void)
{
if (!use_icount) {
@@ -124,7 +123,6 @@ static int64_t qemu_icount_delta(void)
return cpu_get_icount() - cpu_get_clock();
}
}
-#endif
/* enable cpu_get_ticks() */
void cpu_enable_ticks(void)
@@ -1077,9 +1075,17 @@ void quit_timers(void)
int qemu_calculate_timeout(void)
{
-#ifndef CONFIG_IOTHREAD
int timeout;
+#ifdef CONFIG_IOTHREAD
+ /* When using icount, making forward progress with qemu_icount when the
+ guest CPU is idle is critical. We only use the static io-thread timeout
+ for non icount runs. */
+ if (!use_icount) {
+ return 1000;
+ }
+#endif
+
if (!vm_running)
timeout = 5000;
else {
@@ -1110,8 +1116,5 @@ int qemu_calculate_timeout(void)
}
return timeout;
-#else /* CONFIG_IOTHREAD */
- return 1000;
-#endif
}
- [Qemu-devel] MIPS, io-thread, icount and wfi, Edgar E. Iglesias, 2011/01/17
- [Qemu-devel] Re: MIPS, io-thread, icount and wfi,
Edgar E. Iglesias <=
- [Qemu-devel] Re: MIPS, io-thread, icount and wfi, Jan Kiszka, 2011/01/18
- [Qemu-devel] Re: MIPS, io-thread, icount and wfi, Jan Kiszka, 2011/01/18
- [Qemu-devel] Re: MIPS, io-thread, icount and wfi, Marcelo Tosatti, 2011/01/19
- [Qemu-devel] Re: MIPS, io-thread, icount and wfi, Edgar E. Iglesias, 2011/01/19
- [Qemu-devel] Re: MIPS, io-thread, icount and wfi, Edgar E. Iglesias, 2011/01/22