Re: [Qemu-devel] [PATCH 1/4] kvm-all: add kvm_ioctl, kvm_vm_ioctl, kvm_vcpu_ioctl tracepoints

[Eduardo Habkost]

On Fri, May 03, 2013 at 02:12:14PM +0200, Andreas Färber wrote:
> Am 03.05.2013 14:01, schrieb Stefan Hajnoczi:
> > From: Kazuya Saito <address@hidden>
> > 
> > This patch adds tracepoints at ioctl to kvm. Tracing these ioctl is
> > useful for clarification whether the cause of troubles is qemu or kvm.
> > 
> > Signed-off-by: Kazuya Saito <address@hidden>
> > Reviewed-by: Paolo Bonzini <address@hidden>
> > Signed-off-by: Stefan Hajnoczi <address@hidden>
> > ---
> >  kvm-all.c    | 4 ++++
> >  trace-events | 5 +++++
> >  2 files changed, 9 insertions(+)
> > 
> > diff --git a/kvm-all.c b/kvm-all.c
> > index f6c0f4a..4f73b98 100644
> > --- a/kvm-all.c
> > +++ b/kvm-all.c
> > @@ -33,6 +33,7 @@
> >  #include "exec/memory.h"
> >  #include "exec/address-spaces.h"
> >  #include "qemu/event_notifier.h"
> > +#include "trace.h"
> >  
> >  /* This check must be after config-host.h is included */
> >  #ifdef CONFIG_EVENTFD
> > @@ -1687,6 +1688,7 @@ int kvm_ioctl(KVMState *s, int type, ...)
> >      arg = va_arg(ap, void *);
> >      va_end(ap);
> >  
> > +    trace_kvm_ioctl(type, arg);
> >      ret = ioctl(s->fd, type, arg);
> >      if (ret == -1) {
> >          ret = -errno;
> > @@ -1704,6 +1706,7 @@ int kvm_vm_ioctl(KVMState *s, int type, ...)
> >      arg = va_arg(ap, void *);
> >      va_end(ap);
> >  
> > +    trace_kvm_vm_ioctl(type, arg);
> >      ret = ioctl(s->vmfd, type, arg);
> >      if (ret == -1) {
> >          ret = -errno;
> > @@ -1721,6 +1724,7 @@ int kvm_vcpu_ioctl(CPUState *cpu, int type, ...)
> >      arg = va_arg(ap, void *);
> >      va_end(ap);
> >  
> > +    trace_kvm_vcpu_ioctl(cpu->cpu_index, type, arg);
> >      ret = ioctl(cpu->kvm_fd, type, arg);
> >      if (ret == -1) {
> >          ret = -errno;
> > diff --git a/trace-events b/trace-events
> > index 55e80be..d5bc7a5 100644
> > --- a/trace-events
> > +++ b/trace-events
> > @@ -1153,3 +1153,8 @@ virtio_ccw_new_device(int cssid, int ssid, int schid, 
> > int devno, const char *dev
> >  
> >  # migration.c
> >  migrate_set_state(int new_state) "new state %d"
> > +
> > +# kvm-all.c
> > +kvm_ioctl(int type, void *arg) "type %d, arg %p"
> > +kvm_vm_ioctl(int type, void *arg) "type %d, arg %p"
> > +kvm_vcpu_ioctl(int cpu_index, int type, void *arg) "cpu_index %d, type %d, 
> > arg %p"
> 
> Sorry that I'm just seeing this patch now (wasn't CC'ed), but I wonder
> whether cpu_index is the best thing to trace here? Can we still change
> trace event API or would we have to nack/change now?
> 
> CC'ing Igor since he just introduced a cpu_get_arch_id() and there's
> also a kvm_arch_vcpu_id() introduced earlier by Eduardo.

Being kvm_vcpu_ioctl() a very low-level KVM function, I believe the KVM
VCPU "id" (the argument passed to KVM_CREATE_VCPU, that needs to be the
APIC ID on x86, and is returned by kvm_arch_vcpu_id()) is the best CPU
identifier to be included here.

cpu_index is the most ambiguous and least reliable CPU identifier we
have today. I wouldn't use it in any new code.

-- 
Eduardo