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.
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()) {
> /*
>
