Paolo Bonzini <pbonz...@redhat.com> writes:
> On 01/10/19 18:04, Alex Bennée wrote:
>> qemu_cpu_kick is used for a number of reasons including to indicate
>> there is work to be done. However when thread=single the old
>> qemu_cpu_kick_rr_cpu only advanced the vCPU to the next executing one
>> which can lead to a hang in the case that:
>>
>> a) the kick is from outside the vCPUs (e.g. iothread)
>> b) the timers are paused (i.e. iothread calling run_on_cpu)
>>
>> To avoid this lets split qemu_cpu_kick_rr into two functions. One for
>> the timer which continues to advance to the next timeslice and another
>> for all other kicks.
>>
>> Signed-off-by: Alex Bennée <alex.ben...@linaro.org>
>> Cc: Doug Gale <doug...@gmail.com>
>> Cc: Paolo Bonzini <pbonz...@redhat.com>
>> Cc: Peter Maydell <peter.mayd...@linaro.org>
>> ---
>> cpus.c | 24 ++++++++++++++++++------
>> 1 file changed, 18 insertions(+), 6 deletions(-)
>
> Looks good to me. Single-threaded TCG is not going to have high vCPU
> counts anyway.
Are you going to take this via your queue?
>
> Paolo
>
>> diff --git a/cpus.c b/cpus.c
>> index d2c61ff155..bee7209134 100644
>> --- a/cpus.c
>> +++ b/cpus.c
>> @@ -949,8 +949,8 @@ static inline int64_t qemu_tcg_next_kick(void)
>> return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + TCG_KICK_PERIOD;
>> }
>>
>> -/* Kick the currently round-robin scheduled vCPU */
>> -static void qemu_cpu_kick_rr_cpu(void)
>> +/* Kick the currently round-robin scheduled vCPU to next */
>> +static void qemu_cpu_kick_rr_next_cpu(void)
>> {
>> CPUState *cpu;
>> do {
>> @@ -961,6 +961,16 @@ static void qemu_cpu_kick_rr_cpu(void)
>> } while (cpu != atomic_mb_read(&tcg_current_rr_cpu));
>> }
>>
>> +/* Kick all RR vCPUs */
>> +static void qemu_cpu_kick_rr_cpus(void)
>> +{
>> + CPUState *cpu;
>> +
>> + CPU_FOREACH(cpu) {
>> + cpu_exit(cpu);
>> + };
>> +}
>> +
>> static void do_nothing(CPUState *cpu, run_on_cpu_data unused)
>> {
>> }
>> @@ -993,7 +1003,7 @@ void qemu_timer_notify_cb(void *opaque, QEMUClockType
>> type)
>> static void kick_tcg_thread(void *opaque)
>> {
>> timer_mod(tcg_kick_vcpu_timer, qemu_tcg_next_kick());
>> - qemu_cpu_kick_rr_cpu();
>> + qemu_cpu_kick_rr_next_cpu();
>> }
>>
>> static void start_tcg_kick_timer(void)
>> @@ -1828,9 +1838,11 @@ void qemu_cpu_kick(CPUState *cpu)
>> {
>> qemu_cond_broadcast(cpu->halt_cond);
>> if (tcg_enabled()) {
>> - cpu_exit(cpu);
>> - /* NOP unless doing single-thread RR */
>> - qemu_cpu_kick_rr_cpu();
>> + if (qemu_tcg_mttcg_enabled()) {
>> + cpu_exit(cpu);
>> + } else {
>> + qemu_cpu_kick_rr_cpus();
>> + }
>> } else {
>> if (hax_enabled()) {
>> /*
>>
--
Alex Bennée
