Re: [Qemu-devel] [Qemu-ppc] [PATCH v4] ppc: make idle_timer a per-cpu variable

[Greg Kurz]

On Mon, 22 Jul 2019 18:44:24 +1000
David Gibson <address@hidden> wrote:

> On Fri, Jul 19, 2019 at 03:51:26AM -0500, Shivaprasad G Bhat wrote:
> > The current code is broken for more than vcpu as
> > each thread would overwrite idle_timer and there were
> > memory leaks.
> > 
> > Make it part of PowerPCCPU so that every thread has a
> > separate one. Avoid using the timer_new_ns which is
> > not the preferred way to create timers.
> > 
> > Signed-off-by: Shivaprasad G Bhat <address@hidden>
> > Reviewed-by: Greg Kurz <address@hidden>
> 
> So, this looks correct, but..
> 
> ..the whole idle_timer logic is used only in the case that we're
> running with a KVM that doesn't support KVM_CAP_PPC_IRQ_LEVEL.  That
> support appears to have been in since around v2.6.36 some 9 years
> ago.  We could probably just drop support for such old kernels in qemu
> instead.
> 

Ha ! Yes, this is likely the best thing to do :)

> > ---
> >  v3: https://lists.gnu.org/archive/html/qemu-devel/2019-07/msg04375.html
> >  Changes from v3:
> >     - Calling timer_del() before timer_deinit()
> > 
> >  target/ppc/cpu.h |    1 +
> >  target/ppc/kvm.c |   32 +++++++++++++++++---------------
> >  2 files changed, 18 insertions(+), 15 deletions(-)
> > 
> > diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
> > index c9beba2a5c..521086d91a 100644
> > --- a/target/ppc/cpu.h
> > +++ b/target/ppc/cpu.h
> > @@ -1190,6 +1190,7 @@ struct PowerPCCPU {
> >      void *machine_data;
> >      int32_t node_id; /* NUMA node this CPU belongs to */
> >      PPCHash64Options *hash64_opts;
> > +    QEMUTimer idle_timer;
> >  
> >      /* Fields related to migration compatibility hacks */
> >      bool pre_2_8_migration;
> > diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> > index 8a06d3171e..52d3292f45 100644
> > --- a/target/ppc/kvm.c
> > +++ b/target/ppc/kvm.c
> > @@ -87,18 +87,6 @@ static int cap_large_decr;
> >  
> >  static uint32_t debug_inst_opcode;
> >  
> > -/*
> > - * XXX We have a race condition where we actually have a level triggered
> > - *     interrupt, but the infrastructure can't expose that yet, so the 
> > guest
> > - *     takes but ignores it, goes to sleep and never gets notified that 
> > there's
> > - *     still an interrupt pending.
> > - *
> > - *     As a quick workaround, let's just wake up again 20 ms after we 
> > injected
> > - *     an interrupt. That way we can assure that we're always reinjecting
> > - *     interrupts in case the guest swallowed them.
> > - */
> > -static QEMUTimer *idle_timer;
> > -
> >  static void kvm_kick_cpu(void *opaque)
> >  {
> >      PowerPCCPU *cpu = opaque;
> > @@ -491,7 +479,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >          return ret;
> >      }
> >  
> > -    idle_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, kvm_kick_cpu, cpu);
> > +    timer_init_ns(&cpu->idle_timer, QEMU_CLOCK_VIRTUAL, kvm_kick_cpu, cpu);
> >  
> >      switch (cenv->mmu_model) {
> >      case POWERPC_MMU_BOOKE206:
> > @@ -523,6 +511,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >  
> >  int kvm_arch_destroy_vcpu(CPUState *cs)
> >  {
> > +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> > +
> > +    timer_del(&cpu->idle_timer);
> > +    timer_deinit(&cpu->idle_timer);
> > +
> >      return 0;
> >  }
> >  
> > @@ -1379,8 +1372,17 @@ void kvm_arch_pre_run(CPUState *cs, struct kvm_run 
> > *run)
> >              printf("cpu %d fail inject %x\n", cs->cpu_index, irq);
> >          }
> >  
> > -        /* Always wake up soon in case the interrupt was level based */
> > -        timer_mod(idle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
> > +        /*
> > +         * XXX We have a race condition where we actually have a level
> > +         *     triggered interrupt, but the infrastructure can't expose 
> > that
> > +         *     yet, so the guest takes but ignores it, goes to sleep and
> > +         *     never gets notified that there's still an interrupt pending.
> > +         *
> > +         *     As a quick workaround, let's just wake up again 20 ms after
> > +         *     we injected an interrupt. That way we can assure that we're
> > +         *     always reinjecting interrupts in case the guest swallowed 
> > them.
> > +         */
> > +        timer_mod(&cpu->idle_timer, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
> >                         (NANOSECONDS_PER_SECOND / 50));
> >      }
> >  
> > 
>

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