On Sat, Feb 8, 2014 at 9:20 AM, Alex Bligh <a...@alex.org.uk> wrote:
> Paolo,
>
> On 8 Feb 2014, at 13:26, Paolo Bonzini wrote:
>
>>>
>>> What I'd suggest you do is run qemu within gdb, and when you have
>>> seen the sluggish behaviour, set a breakpoint in timerlist_run_timers
>>> just before the line saying cb(opaque). If I'm right your breakpoint
>>> should immediately hit. Step in to the callback and note which it is.
>>> It should always (or nearly always) be the same timer (note the process
>>> of debugging will cause other timers to expire).
>>
>> Alex, could you add a trace event to timerlist_run_timers and mod_timer?
>> For timerlist_run_timer it should include the timer (ts), the callback and
>> the opaque value.
>>
>> This would make it simpler to find if this is the cause, and to debug it
>> without introducing as much perturbation.
>
> A while ago a wrote some instrumentation. I can't recall how far I got with
> testing it, but here it is rebased onto master without so much as a compile
> test
> (top 4 commits - ignore the 5th):
>
> https://github.com/abligh/qemu/commit/e711816da9831c97f7d8a111b610ef42f7ba69fa
This doesn't appear to be too useful. The AvgLength is large because
INT64_MAX / GTIMER_SCALE is used as the next timer value when no timer
is needed. I also changed the code to just call timer_del instead of
setting a max timeout and the length looks normal (~10ms).
Timer list at 0x7fae6463d680 clock 1:
Address Expiries AvgLength NumShort Source
0x7fae646659e0 673 13704855334071269 0 cpu.c:229
0x7fae646650f0 691 -6386455212 0 cpu.c:229
0x7fae6480e630 1 4294967294556 0 ptimer.c:229
This seems to be more related to interaction between the 2 timers as
the same timer works fine for single core use. The relevant code is
target-arm/helper.c:gt_recalc_timer.
I did find one bug that would seem to cause interrupts to be missed or
fire twice, but it didn't make any difference:
diff --git a/target-arm/helper.c b/target-arm/helper.c
index ca5b000..325515f 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -905,7 +905,7 @@ static int gt_ctl_write(CPUARMState *env, const
ARMCPRegInfo *ri,
if ((oldval ^ value) & 1) {
/* Enable toggled */
gt_recalc_timer(cpu, timeridx);
- } else if ((oldval & value) & 2) {
+ } else if ((oldval ^ value) & 2) {
/* IMASK toggled: don't need to recalculate,
* just set the interrupt line based on ISTATUS
*/
Rob
