| Message ID | 20200728141005.28664-3-alex.bennee@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | clean-ups for sleep=off behaviour | expand |
On Tue, 28 Jul 2020 at 15:10, Alex Bennée <alex.bennee@linaro.org> wrote: > > Otherwise we have an unfortunate interaction with -count sleep=off > which means we fast forward time when we don't need to. The easiest > way to trigger it was to attach to the gdbstub and place a break point > at the timers IRQ routine. Once the timer fired setting the next event > at INT_MAX then qemu_start_warp_timer would skip to the end. > > Signed-off-by: Alex Bennée <alex.bennee@linaro.org> > --- > target/arm/helper.c | 35 ++++++++++++++++++++++------------- > 1 file changed, 22 insertions(+), 13 deletions(-) > > diff --git a/target/arm/helper.c b/target/arm/helper.c > index c69a2baf1d3..ec1b84cf0fd 100644 > --- a/target/arm/helper.c > +++ b/target/arm/helper.c > @@ -2683,7 +2683,7 @@ static void gt_recalc_timer(ARMCPU *cpu, int timeridx) > uint64_t count = gt_get_countervalue(&cpu->env); > /* Note that this must be unsigned 64 bit arithmetic: */ > int istatus = count - offset >= gt->cval; > - uint64_t nexttick; > + uint64_t nexttick = 0; > int irqstate; > > gt->ctl = deposit32(gt->ctl, 2, 1, istatus); > @@ -2692,21 +2692,30 @@ static void gt_recalc_timer(ARMCPU *cpu, int timeridx) > qemu_set_irq(cpu->gt_timer_outputs[timeridx], irqstate); > > if (istatus) { > - /* Next transition is when count rolls back over to zero */ > - nexttick = UINT64_MAX; > + /* > + * The IRQ status of the timer will persist until: > + * - CVAL is changed or > + * - ENABLE is changed > + * > + * There is no point re-arming the timer for some far > + * flung future - currently it just is. > + */ > + timer_del(cpu->gt_timer[timeridx]); Why do we delete the timer for this case of "next time we need to know is massively in the future"... > } else { > /* Next transition is when we hit cval */ > nexttick = gt->cval + offset; > - } > - /* Note that the desired next expiry time might be beyond the > - * signed-64-bit range of a QEMUTimer -- in this case we just > - * set the timer for as far in the future as possible. When the > - * timer expires we will reset the timer for any remaining period. > - */ > - if (nexttick > INT64_MAX / gt_cntfrq_period_ns(cpu)) { > - timer_mod_ns(cpu->gt_timer[timeridx], INT64_MAX); > - } else { > - timer_mod(cpu->gt_timer[timeridx], nexttick); > + > + /* > + * It is possible the next tick is beyond the > + * signed-64-bit range of a QEMUTimer but currently the > + * timer system doesn't support a run time of more the 292 > + * odd years so we set it to INT_MAX in this case. > + */ > + if (nexttick > INT64_MAX / gt_cntfrq_period_ns(cpu)) { > + timer_mod_ns(cpu->gt_timer[timeridx], INT64_MAX); ...but here we handle the similar case by "set a timeout for INT64_MAX" ? > + } else { > + timer_mod(cpu->gt_timer[timeridx], nexttick); > + } > } > trace_arm_gt_recalc(timeridx, irqstate, nexttick); > } else { > -- thanks -- PMM
Peter Maydell <peter.maydell@linaro.org> writes: > On Tue, 28 Jul 2020 at 15:10, Alex Bennée <alex.bennee@linaro.org> wrote: >> >> Otherwise we have an unfortunate interaction with -count sleep=off >> which means we fast forward time when we don't need to. The easiest >> way to trigger it was to attach to the gdbstub and place a break point >> at the timers IRQ routine. Once the timer fired setting the next event >> at INT_MAX then qemu_start_warp_timer would skip to the end. >> >> Signed-off-by: Alex Bennée <alex.bennee@linaro.org> >> --- >> target/arm/helper.c | 35 ++++++++++++++++++++++------------- >> 1 file changed, 22 insertions(+), 13 deletions(-) >> >> diff --git a/target/arm/helper.c b/target/arm/helper.c >> index c69a2baf1d3..ec1b84cf0fd 100644 >> --- a/target/arm/helper.c >> +++ b/target/arm/helper.c >> @@ -2683,7 +2683,7 @@ static void gt_recalc_timer(ARMCPU *cpu, int timeridx) >> uint64_t count = gt_get_countervalue(&cpu->env); >> /* Note that this must be unsigned 64 bit arithmetic: */ >> int istatus = count - offset >= gt->cval; >> - uint64_t nexttick; >> + uint64_t nexttick = 0; >> int irqstate; >> >> gt->ctl = deposit32(gt->ctl, 2, 1, istatus); >> @@ -2692,21 +2692,30 @@ static void gt_recalc_timer(ARMCPU *cpu, int timeridx) >> qemu_set_irq(cpu->gt_timer_outputs[timeridx], irqstate); >> >> if (istatus) { >> - /* Next transition is when count rolls back over to zero */ >> - nexttick = UINT64_MAX; >> + /* >> + * The IRQ status of the timer will persist until: >> + * - CVAL is changed or >> + * - ENABLE is changed >> + * >> + * There is no point re-arming the timer for some far >> + * flung future - currently it just is. >> + */ >> + timer_del(cpu->gt_timer[timeridx]); > > Why do we delete the timer for this case of "next time we need to > know is massively in the future"... It's not really - it's happening now and it will continue to happen until the IRQ is serviced or we change the CVAL at which point we can calculate the next time we need it. > >> } else { >> /* Next transition is when we hit cval */ >> nexttick = gt->cval + offset; >> - } >> - /* Note that the desired next expiry time might be beyond the >> - * signed-64-bit range of a QEMUTimer -- in this case we just >> - * set the timer for as far in the future as possible. When the >> - * timer expires we will reset the timer for any remaining period. >> - */ >> - if (nexttick > INT64_MAX / gt_cntfrq_period_ns(cpu)) { >> - timer_mod_ns(cpu->gt_timer[timeridx], INT64_MAX); >> - } else { >> - timer_mod(cpu->gt_timer[timeridx], nexttick); >> + >> + /* >> + * It is possible the next tick is beyond the >> + * signed-64-bit range of a QEMUTimer but currently the >> + * timer system doesn't support a run time of more the 292 >> + * odd years so we set it to INT_MAX in this case. >> + */ >> + if (nexttick > INT64_MAX / gt_cntfrq_period_ns(cpu)) { >> + timer_mod_ns(cpu->gt_timer[timeridx], INT64_MAX); > > ...but here we handle the similar case by "set a timeout for > INT64_MAX" ? Yeah we could just swallow it up and report something to say it's not going to happen because it's beyond the horizon of what QEMUTimer can deal with. > >> + } else { >> + timer_mod(cpu->gt_timer[timeridx], nexttick); >> + } >> } >> trace_arm_gt_recalc(timeridx, irqstate, nexttick); >> } else { >> -- > > thanks > -- PMM -- Alex Bennée
On Tue, 28 Jul 2020 at 17:11, Alex Bennée <alex.bennee@linaro.org> wrote: > > > Peter Maydell <peter.maydell@linaro.org> writes: > > > On Tue, 28 Jul 2020 at 15:10, Alex Bennée <alex.bennee@linaro.org> wrote: > >> > >> Otherwise we have an unfortunate interaction with -count sleep=off > >> which means we fast forward time when we don't need to. The easiest > >> way to trigger it was to attach to the gdbstub and place a break point > >> at the timers IRQ routine. Once the timer fired setting the next event > >> at INT_MAX then qemu_start_warp_timer would skip to the end. > >> > >> Signed-off-by: Alex Bennée <alex.bennee@linaro.org> > >> --- > >> if (istatus) { > >> - /* Next transition is when count rolls back over to zero */ > >> - nexttick = UINT64_MAX; > >> + /* > >> + * The IRQ status of the timer will persist until: > >> + * - CVAL is changed or > >> + * - ENABLE is changed > >> + * > >> + * There is no point re-arming the timer for some far > >> + * flung future - currently it just is. > >> + */ > >> + timer_del(cpu->gt_timer[timeridx]); > > > > Why do we delete the timer for this case of "next time we need to > > know is massively in the future"... > > It's not really - it's happening now and it will continue to happen > until the IRQ is serviced or we change the CVAL at which point we can > calculate the next time we need it. It is far-future: the counter can roll all the way round and back over to zero, as the old comment states. (Other reasons for things to change get handled via other code paths: it's only the "at some defined time in the future a change happens" cases that we need to set a timer for). It's the same situation as below, I think (though I don't know why we used UINT64_MAX for one and INT64_MAX for the other). -- PMM
diff --git a/target/arm/helper.c b/target/arm/helper.c index c69a2baf1d3..ec1b84cf0fd 100644 --- a/target/arm/helper.c +++ b/target/arm/helper.c @@ -2683,7 +2683,7 @@ static void gt_recalc_timer(ARMCPU *cpu, int timeridx) uint64_t count = gt_get_countervalue(&cpu->env); /* Note that this must be unsigned 64 bit arithmetic: */ int istatus = count - offset >= gt->cval; - uint64_t nexttick; + uint64_t nexttick = 0; int irqstate; gt->ctl = deposit32(gt->ctl, 2, 1, istatus); @@ -2692,21 +2692,30 @@ static void gt_recalc_timer(ARMCPU *cpu, int timeridx) qemu_set_irq(cpu->gt_timer_outputs[timeridx], irqstate); if (istatus) { - /* Next transition is when count rolls back over to zero */ - nexttick = UINT64_MAX; + /* + * The IRQ status of the timer will persist until: + * - CVAL is changed or + * - ENABLE is changed + * + * There is no point re-arming the timer for some far + * flung future - currently it just is. + */ + timer_del(cpu->gt_timer[timeridx]); } else { /* Next transition is when we hit cval */ nexttick = gt->cval + offset; - } - /* Note that the desired next expiry time might be beyond the - * signed-64-bit range of a QEMUTimer -- in this case we just - * set the timer for as far in the future as possible. When the - * timer expires we will reset the timer for any remaining period. - */ - if (nexttick > INT64_MAX / gt_cntfrq_period_ns(cpu)) { - timer_mod_ns(cpu->gt_timer[timeridx], INT64_MAX); - } else { - timer_mod(cpu->gt_timer[timeridx], nexttick); + + /* + * It is possible the next tick is beyond the + * signed-64-bit range of a QEMUTimer but currently the + * timer system doesn't support a run time of more the 292 + * odd years so we set it to INT_MAX in this case. + */ + if (nexttick > INT64_MAX / gt_cntfrq_period_ns(cpu)) { + timer_mod_ns(cpu->gt_timer[timeridx], INT64_MAX); + } else { + timer_mod(cpu->gt_timer[timeridx], nexttick); + } } trace_arm_gt_recalc(timeridx, irqstate, nexttick); } else {
Otherwise we have an unfortunate interaction with -count sleep=off which means we fast forward time when we don't need to. The easiest way to trigger it was to attach to the gdbstub and place a break point at the timers IRQ routine. Once the timer fired setting the next event at INT_MAX then qemu_start_warp_timer would skip to the end. Signed-off-by: Alex Bennée <alex.bennee@linaro.org> --- target/arm/helper.c | 35 ++++++++++++++++++++++------------- 1 file changed, 22 insertions(+), 13 deletions(-) -- 2.20.1