| Message ID | 1464986428-6739-13-git-send-email-alex.bennee@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 03/06/16 23:40, Alex Bennée wrote: > diff --git a/cpus.c b/cpus.c > index 1694ce9..12e04c9 100644 > --- a/cpus.c > +++ b/cpus.c > @@ -1208,9 +1208,29 @@ static int tcg_cpu_exec(CPUState *cpu) > return ret; > } > > +/* Single-threaded TCG > + * > + * In the single-threaded case each vCPU is simulated in turn. If > + * there is more than a single vCPU we create a simple timer to kick > + * the vCPU and ensure we don't get stuck in a tight loop in one vCPU. > + * This is done explicitly rather than relying on side-effects > + * elsewhere. > + */ > +static void qemu_cpu_kick_no_halt(void); > +#define TCG_KICK_FREQ (qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + \ > + NANOSECONDS_PER_SECOND / 10) Hmm, it doesn't look nice to wrap calculation of the next timeout in a macro and name it '*_FREQ'. I think we'd better do like this: #define TCG_KICK_PERIOD (NANOSECONDS_PER_SECOND / 10) static inline int64_t qemu_tcg_next_kick(void) { return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD; } and use it like this: timer_mod(kick_timer, qemu_tcg_next_kick()); Kind regards, Sergey > + > +static void kick_tcg_thread(void *opaque) > +{ > + QEMUTimer *self = *(QEMUTimer **) opaque; > + timer_mod(self, TCG_KICK_FREQ); > + qemu_cpu_kick_no_halt(); > +} > + > static void *qemu_tcg_cpu_thread_fn(void *arg) > { > CPUState *cpu = arg; > + QEMUTimer *kick_timer; > > rcu_register_thread(); > > @@ -1234,6 +1254,13 @@ static void *qemu_tcg_cpu_thread_fn(void *arg) > } > } > > + /* Set to kick if we have to do more than one vCPU */ > + if (CPU_NEXT(first_cpu)) { > + kick_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, kick_tcg_thread, > + &kick_timer); > + timer_mod(kick_timer, TCG_KICK_FREQ); > + } > + > /* process any pending work */ > atomic_mb_set(&exit_request, 1); >
On 06/27/2016 02:20 PM, Sergey Fedorov wrote: > On 03/06/16 23:40, Alex Bennée wrote: >> diff --git a/cpus.c b/cpus.c >> index 1694ce9..12e04c9 100644 >> --- a/cpus.c >> +++ b/cpus.c >> @@ -1208,9 +1208,29 @@ static int tcg_cpu_exec(CPUState *cpu) >> return ret; >> } >> >> +/* Single-threaded TCG >> + * >> + * In the single-threaded case each vCPU is simulated in turn. If >> + * there is more than a single vCPU we create a simple timer to kick >> + * the vCPU and ensure we don't get stuck in a tight loop in one vCPU. >> + * This is done explicitly rather than relying on side-effects >> + * elsewhere. >> + */ >> +static void qemu_cpu_kick_no_halt(void); >> +#define TCG_KICK_FREQ (qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + \ >> + NANOSECONDS_PER_SECOND / 10) > > Hmm, it doesn't look nice to wrap calculation of the next timeout in a > macro and name it '*_FREQ'. I think we'd better do like this: > > #define TCG_KICK_PERIOD (NANOSECONDS_PER_SECOND / 10) > > static inline int64_t qemu_tcg_next_kick(void) > { > return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD; > } > > and use it like this: > > timer_mod(kick_timer, qemu_tcg_next_kick()); Agreed. As an aside, surely a period of 10ns is too small. That's on the order of 20-50 host instructions. r~
On 02/07/16 03:17, Richard Henderson wrote: > On 06/27/2016 02:20 PM, Sergey Fedorov wrote: >> On 03/06/16 23:40, Alex Bennée wrote: >>> diff --git a/cpus.c b/cpus.c >>> index 1694ce9..12e04c9 100644 >>> --- a/cpus.c >>> +++ b/cpus.c >>> @@ -1208,9 +1208,29 @@ static int tcg_cpu_exec(CPUState *cpu) >>> return ret; >>> } >>> >>> +/* Single-threaded TCG >>> + * >>> + * In the single-threaded case each vCPU is simulated in turn. If >>> + * there is more than a single vCPU we create a simple timer to kick >>> + * the vCPU and ensure we don't get stuck in a tight loop in one vCPU. >>> + * This is done explicitly rather than relying on side-effects >>> + * elsewhere. >>> + */ >>> +static void qemu_cpu_kick_no_halt(void); >>> +#define TCG_KICK_FREQ (qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + \ >>> + NANOSECONDS_PER_SECOND / 10) >> >> Hmm, it doesn't look nice to wrap calculation of the next timeout in a >> macro and name it '*_FREQ'. I think we'd better do like this: >> >> #define TCG_KICK_PERIOD (NANOSECONDS_PER_SECOND / 10) >> >> static inline int64_t qemu_tcg_next_kick(void) >> { >> return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD; >> } >> >> and use it like this: >> >> timer_mod(kick_timer, qemu_tcg_next_kick()); > > Agreed. > > As an aside, surely a period of 10ns is too small. > That's on the order of 20-50 host instructions. I think the period is 10 times in a second which is 100 ms. Regards, Sergey
diff --git a/cpus.c b/cpus.c index 1694ce9..12e04c9 100644 --- a/cpus.c +++ b/cpus.c @@ -1208,9 +1208,29 @@ static int tcg_cpu_exec(CPUState *cpu) return ret; } +/* Single-threaded TCG + * + * In the single-threaded case each vCPU is simulated in turn. If + * there is more than a single vCPU we create a simple timer to kick + * the vCPU and ensure we don't get stuck in a tight loop in one vCPU. + * This is done explicitly rather than relying on side-effects + * elsewhere. + */ +static void qemu_cpu_kick_no_halt(void); +#define TCG_KICK_FREQ (qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + \ + NANOSECONDS_PER_SECOND / 10) + +static void kick_tcg_thread(void *opaque) +{ + QEMUTimer *self = *(QEMUTimer **) opaque; + timer_mod(self, TCG_KICK_FREQ); + qemu_cpu_kick_no_halt(); +} + static void *qemu_tcg_cpu_thread_fn(void *arg) { CPUState *cpu = arg; + QEMUTimer *kick_timer; rcu_register_thread(); @@ -1234,6 +1254,13 @@ static void *qemu_tcg_cpu_thread_fn(void *arg) } } + /* Set to kick if we have to do more than one vCPU */ + if (CPU_NEXT(first_cpu)) { + kick_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, kick_tcg_thread, + &kick_timer); + timer_mod(kick_timer, TCG_KICK_FREQ); + } + /* process any pending work */ atomic_mb_set(&exit_request, 1);
Currently we rely on the side effect of the main loop grabbing the iothread_mutex to give any long running basic block chains a kick to ensure the next vCPU is scheduled. As this code is being re-factored and rationalised we now do it explicitly here. Signed-off-by: Alex Bennée <alex.bennee@linaro.org> --- v2 - re-base fixes - get_ticks_per_sec() -> NANOSECONDS_PER_SEC v3 - add define for TCG_KICK_FREQ - fix checkpatch warning --- cpus.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+)