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main: force enabling of I/O thread

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Enabling the I/O thread by default seems like an important part of declaring
1.0.  Besides allowing true SMP support with KVM, the I/O thread means that the
TCG VCPU doesn't have to multiplex itself with the I/O dispatch routines which
currently requires a (racey) signal based alarm system.

I know there have been concerns about performance.  I think so far the ones that
have come up (virtio-net) are most likely due to secondary reasons like
decreased batching.

I think we ought to force enabling I/O thread early in 1.0 development and
commit to resolving any lingering issues.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Anthony Liguori
2011-08-22 08:24:58 -05:00
parent d9cd446b4f
commit 12d4536f7d
6 changed files with 1 additions and 232 deletions
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53
qemu-timer.c
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@@ -101,22 +101,6 @@ static int64_t cpu_get_clock(void)
}
}
#ifndef CONFIG_IOTHREAD
static int64_t qemu_icount_delta(void)
{
if (!use_icount) {
return 5000 * (int64_t) 1000000;
} else if (use_icount == 1) {
/* When not using an adaptive execution frequency
we tend to get badly out of sync with real time,
so just delay for a reasonable amount of time. */
return 0;
} else {
return cpu_get_icount() - cpu_get_clock();
}
}
#endif
/* enable cpu_get_ticks() */
void cpu_enable_ticks(void)
{
@@ -688,9 +672,7 @@ void configure_icount(const char *option)
if (!option)
return;
#ifdef CONFIG_IOTHREAD
vm_clock->warp_timer = qemu_new_timer_ns(rt_clock, icount_warp_rt, NULL);
#endif
if (strcmp(option, "auto") != 0) {
icount_time_shift = strtol(option, NULL, 0);
@@ -1178,41 +1160,6 @@ void quit_timers(void)
int qemu_calculate_timeout(void)
{
#ifndef CONFIG_IOTHREAD
int timeout;
if (!vm_running)
timeout = 5000;
else {
/* XXX: use timeout computed from timers */
int64_t add;
int64_t delta;
/* Advance virtual time to the next event. */
delta = qemu_icount_delta();
if (delta > 0) {
/* If virtual time is ahead of real time then just
wait for IO. */
timeout = (delta + 999999) / 1000000;
} else {
/* Wait for either IO to occur or the next
timer event. */
add = qemu_next_icount_deadline();
/* We advance the timer before checking for IO.
Limit the amount we advance so that early IO
activity won't get the guest too far ahead. */
if (add > 10000000)
add = 10000000;
delta += add;
qemu_icount += qemu_icount_round (add);
timeout = delta / 1000000;
if (timeout < 0)
timeout = 0;
}
}
return timeout;
#else /* CONFIG_IOTHREAD */
return 1000;
#endif
}