[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 1/2] Correct alarm deadline computation
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [PATCH 1/2] Correct alarm deadline computation |
Date: |
Sun, 30 Jan 2011 17:46:43 +0100 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Sat, Jan 29, 2011 at 12:00:47PM +0100, Paolo Bonzini wrote:
> When the QEMU_CLOCK_HOST clock was added, computation of its
> deadline was added to qemu_next_deadline, which is correct but
> incomplete.
>
> I noticed this while trying to make sense of the rules whereby
> qemu_next_deadline_dyntick is computed, which miss QEMU_CLOCK_HOST
> when use_icount is true. Looking at the history showed this to
> be just an oversight, as the next patch shows clearly.
>
> This patch inlines qemu_next_deadline into qemu_next_deadline_dyntick,
> and corrects the logic so that only QEMU_CLOCK_VIRTUAL is skipped for
> use_icount == true.
>
> Signed-off-by: Paolo Bonzini <address@hidden>
> Cc: Jan Kiszka <address@hidden>
> ---
> qemu-timer.c | 15 +++++++++++----
> 1 files changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/qemu-timer.c b/qemu-timer.c
> index db1ec49..174fd0c 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -724,11 +724,18 @@ static uint64_t qemu_next_deadline_dyntick(void)
> int64_t delta;
> int64_t rtdelta;
>
> - if (use_icount)
> + if (!use_icount && active_timers[QEMU_CLOCK_VIRTUAL]) {
> + delta = active_timers[QEMU_CLOCK_VIRTUAL]->expire_time -
> + qemu_get_clock(vm_clock);
> + } else {
> delta = INT32_MAX;
> - else
> - delta = (qemu_next_deadline() + 999) / 1000;
> -
This computation handled the fact that the value is returned in ns, and
we want us.
> + }
> + if (active_timers[QEMU_CLOCK_HOST]) {
> + int64_t hdelta = active_timers[QEMU_CLOCK_HOST]->expire_time -
> + qemu_get_clock(host_clock);
> + if (hdelta < delta)
> + delta = hdelta;
> + }
And this doesn't appear anymore after your changes.
> if (active_timers[QEMU_CLOCK_REALTIME]) {
> rtdelta = (active_timers[QEMU_CLOCK_REALTIME]->expire_time -
> qemu_get_clock(rt_clock))*1000;
Here we multiply because the value is returned in ms and we want us.
IMHO we should just use qemu_get_clock_ns() instead, replace
MIN_TIMER_REARM_US by MIN_TIMER_REARM_NS, and return a ns value
instead. Of course dynticks_rearm_timer() has to be adjusted, but it
should not be problematic given it uses ns internally.
Otherwise good catch, the issue is real, and the way to fix it looks
correct.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
address@hidden http://www.aurel32.net