[PATCH V7 01/18] perf/core: Use static_call to optimize perf_guest_info_callbacks

[Mark Rutland]

On Fri, Jul 02, 2021 at 09:00:22AM -0700, Joe Perches wrote:
> On Fri, 2021-07-02 at 13:22 +0200, Peter Zijlstra wrote:
> > On Tue, Jun 22, 2021 at 05:42:49PM +0800, Zhu Lingshan wrote:
> > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> []
> > > @@ -90,6 +90,27 @@ DEFINE_STATIC_CALL_NULL(x86_pmu_pebs_aliases, *x86_pmu.pebs_aliases);
> > >   */
> > >  DEFINE_STATIC_CALL_RET0(x86_pmu_guest_get_msrs, *x86_pmu.guest_get_msrs);
> > >  
> > > 
> > > +DEFINE_STATIC_CALL_RET0(x86_guest_state, *(perf_guest_cbs->state));
> > > +DEFINE_STATIC_CALL_RET0(x86_guest_get_ip, *(perf_guest_cbs->get_ip));
> > > +DEFINE_STATIC_CALL_RET0(x86_guest_handle_intel_pt_intr, *(perf_guest_cbs->handle_intel_pt_intr));
> > > +
> > > +void arch_perf_update_guest_cbs(void)
> > > +{
> > > +	static_call_update(x86_guest_state, (void *)&__static_call_return0);
> > > +	static_call_update(x86_guest_get_ip, (void *)&__static_call_return0);
> > > +	static_call_update(x86_guest_handle_intel_pt_intr, (void *)&__static_call_return0);
> > > +
> > > +	if (perf_guest_cbs && perf_guest_cbs->state)
> > > +		static_call_update(x86_guest_state, perf_guest_cbs->state);
> > > +
> > > +	if (perf_guest_cbs && perf_guest_cbs->get_ip)
> > > +		static_call_update(x86_guest_get_ip, perf_guest_cbs->get_ip);
> > > +
> > > +	if (perf_guest_cbs && perf_guest_cbs->handle_intel_pt_intr)
> > > +		static_call_update(x86_guest_handle_intel_pt_intr,
> > > +				   perf_guest_cbs->handle_intel_pt_intr);
> > > +}
> > 
> > Coding style wants { } on that last if().
> 
> That's just your personal preference.
> 
> The coding-style document doesn't require that.
> 
> It just says single statement.  It's not the number of
> vertical lines or characters required for the statement.
> 
> ----------------------------------
> 
> Do not unnecessarily use braces where a single statement will do.
> 
> .. code-block:: c
> 
> 	if (condition)
> 		action();
> 
> and
> 
> .. code-block:: none
> 
> 	if (condition)
> 		do_this();
> 	else
> 		do_that();
> 
> This does not apply if only one branch of a conditional statement is a single
> statement; in the latter case use braces in both branches:

Immediately after this, we say:

| Also, use braces when a loop contains more than a single simple statement:
|
| .. code-block:: c
| 
|         while (condition) {
|                 if (test)
|                         do_something();
|         }
| 

... and while that says "a loop", the principle is obviously supposed to
apply to conditionals too; structurally they're no different. We should
just fix the documentation to say "a loop or conditional", or something
to that effect.

Mark.