diff mbox series

[v7,4/5] x86: perf: Refactor misc flag assignments

Message ID 20241107190336.2963882-5-coltonlewis@google.com (mailing list archive)
State New
Headers show
Series Correct perf sampling with Guest VMs | expand

Commit Message

Colton Lewis Nov. 7, 2024, 7:03 p.m. UTC 
Break the assignment logic for misc flags into their own respective
functions to reduce the complexity of the nested logic.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/x86/events/core.c            | 32 +++++++++++++++++++++++--------
 arch/x86/include/asm/perf_event.h |  2 ++
 2 files changed, 26 insertions(+), 8 deletions(-)

Comments

Liang, Kan Nov. 7, 2024, 7:40 p.m. UTC | #1 
On 2024-11-07 2:03 p.m., Colton Lewis wrote:
> Break the assignment logic for misc flags into their own respective
> functions to reduce the complexity of the nested logic.
> 
> Signed-off-by: Colton Lewis <coltonlewis@google.com>
> Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
> ---

Acked-by: Kan Liang <kan.liang@linux.intel.com>

Thanks,
Kan
>  arch/x86/events/core.c            | 32 +++++++++++++++++++++++--------
>  arch/x86/include/asm/perf_event.h |  2 ++
>  2 files changed, 26 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index d19e939f3998..9fdc5fa22c66 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -3011,16 +3011,35 @@ unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)
>  	return regs->ip + code_segment_base(regs);
>  }
>  
> +static unsigned long common_misc_flags(struct pt_regs *regs)
> +{
> +	if (regs->flags & PERF_EFLAGS_EXACT)
> +		return PERF_RECORD_MISC_EXACT_IP;
> +
> +	return 0;
> +}
> +
> +unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
> +{
> +	unsigned long guest_state = perf_guest_state();
> +	unsigned long flags = common_misc_flags(regs);
> +
> +	if (!(guest_state & PERF_GUEST_ACTIVE))
> +		return flags;
> +
> +	if (guest_state & PERF_GUEST_USER)
> +		return flags & PERF_RECORD_MISC_GUEST_USER;
> +	else
> +		return flags & PERF_RECORD_MISC_GUEST_KERNEL;
> +}
> +
>  unsigned long perf_arch_misc_flags(struct pt_regs *regs)
>  {
>  	unsigned int guest_state = perf_guest_state();
> -	int misc = 0;
> +	unsigned long misc = common_misc_flags(regs);
>  
>  	if (guest_state) {
> -		if (guest_state & PERF_GUEST_USER)
> -			misc |= PERF_RECORD_MISC_GUEST_USER;
> -		else
> -			misc |= PERF_RECORD_MISC_GUEST_KERNEL;
> +		misc |= perf_arch_guest_misc_flags(regs);
>  	} else {
>  		if (user_mode(regs))
>  			misc |= PERF_RECORD_MISC_USER;
> @@ -3028,9 +3047,6 @@ unsigned long perf_arch_misc_flags(struct pt_regs *regs)
>  			misc |= PERF_RECORD_MISC_KERNEL;
>  	}
>  
> -	if (regs->flags & PERF_EFLAGS_EXACT)
> -		misc |= PERF_RECORD_MISC_EXACT_IP;
> -
>  	return misc;
>  }
>  
> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> index feb87bf3d2e9..d95f902acc52 100644
> --- a/arch/x86/include/asm/perf_event.h
> +++ b/arch/x86/include/asm/perf_event.h
> @@ -538,7 +538,9 @@ struct x86_perf_regs {
>  
>  extern unsigned long perf_arch_instruction_pointer(struct pt_regs *regs);
>  extern unsigned long perf_arch_misc_flags(struct pt_regs *regs);
> +extern unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs);
>  #define perf_arch_misc_flags(regs)	perf_arch_misc_flags(regs)
> +#define perf_arch_guest_misc_flags(regs)	perf_arch_guest_misc_flags(regs)
>  
>  #include <asm/stacktrace.h>
>
Peter Zijlstra Nov. 8, 2024, 3:34 p.m. UTC | #2 
On Thu, Nov 07, 2024 at 07:03:35PM +0000, Colton Lewis wrote:
> Break the assignment logic for misc flags into their own respective
> functions to reduce the complexity of the nested logic.
> 
> Signed-off-by: Colton Lewis <coltonlewis@google.com>
> Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
> ---
>  arch/x86/events/core.c            | 32 +++++++++++++++++++++++--------
>  arch/x86/include/asm/perf_event.h |  2 ++
>  2 files changed, 26 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index d19e939f3998..9fdc5fa22c66 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -3011,16 +3011,35 @@ unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)
>  	return regs->ip + code_segment_base(regs);
>  }
>  
> +static unsigned long common_misc_flags(struct pt_regs *regs)
> +{
> +	if (regs->flags & PERF_EFLAGS_EXACT)
> +		return PERF_RECORD_MISC_EXACT_IP;
> +
> +	return 0;
> +}
> +
> +unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
> +{
> +	unsigned long guest_state = perf_guest_state();
> +	unsigned long flags = common_misc_flags(regs);

This is double common_misc and makes no sense

> +
> +	if (!(guest_state & PERF_GUEST_ACTIVE))
> +		return flags;
> +
> +	if (guest_state & PERF_GUEST_USER)
> +		return flags & PERF_RECORD_MISC_GUEST_USER;
> +	else
> +		return flags & PERF_RECORD_MISC_GUEST_KERNEL;

And this is just broken garbage, right?

> +}

Did you mean to write:

unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
{
	unsigned long guest_state = perf_guest_state();
	unsigned long flags = 0;

	if (guest_state & PERF_GUEST_ACTIVE) {
		if (guest_state & PERF_GUEST_USER)
			flags |= PERF_RECORD_MISC_GUEST_USER;
		else
			flags |= PERF_RECORD_MISC_GUEST_KERNEL;
	}

	return flags;
}

>  unsigned long perf_arch_misc_flags(struct pt_regs *regs)
>  {
>  	unsigned int guest_state = perf_guest_state();
> -	int misc = 0;
> +	unsigned long misc = common_misc_flags(regs);

Because here you do the common thing..

>  
>  	if (guest_state) {
> -		if (guest_state & PERF_GUEST_USER)
> -			misc |= PERF_RECORD_MISC_GUEST_USER;
> -		else
> -			misc |= PERF_RECORD_MISC_GUEST_KERNEL;
> +		misc |= perf_arch_guest_misc_flags(regs);

And here you mix in the guest things.

>  	} else {
>  		if (user_mode(regs))
>  			misc |= PERF_RECORD_MISC_USER;
Peter Zijlstra Nov. 8, 2024, 7:20 p.m. UTC | #3 
On Fri, Nov 08, 2024 at 07:01:16PM +0000, Colton Lewis wrote:
> Peter Zijlstra <peterz@infradead.org> writes:
> 
> > On Thu, Nov 07, 2024 at 07:03:35PM +0000, Colton Lewis wrote:
> > > Break the assignment logic for misc flags into their own respective
> > > functions to reduce the complexity of the nested logic.
> 
> > > Signed-off-by: Colton Lewis <coltonlewis@google.com>
> > > Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
> > > ---
> > >   arch/x86/events/core.c            | 32 +++++++++++++++++++++++--------
> > >   arch/x86/include/asm/perf_event.h |  2 ++
> > >   2 files changed, 26 insertions(+), 8 deletions(-)
> 
> > > diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> > > index d19e939f3998..9fdc5fa22c66 100644
> > > --- a/arch/x86/events/core.c
> > > +++ b/arch/x86/events/core.c
> > > @@ -3011,16 +3011,35 @@ unsigned long
> > > perf_arch_instruction_pointer(struct pt_regs *regs)
> > >   	return regs->ip + code_segment_base(regs);
> > >   }
> 
> > > +static unsigned long common_misc_flags(struct pt_regs *regs)
> > > +{
> > > +	if (regs->flags & PERF_EFLAGS_EXACT)
> > > +		return PERF_RECORD_MISC_EXACT_IP;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
> > > +{
> > > +	unsigned long guest_state = perf_guest_state();
> > > +	unsigned long flags = common_misc_flags(regs);
> 
> > This is double common_misc and makes no sense
> 
> I'm confused what you mean. Are you referring to starting with
> common_misc_flags in both perf_arch_misc_flags and
> perf_arch_guest_misc_flags so possibly the common_msic_flags are set
> twice?
> 
> That seems like a good thing that common flags are set wherever they
> apply. You can't guarantee where perf_arch_guest_misc_flags may be
> called in the future.

I got confused by perf_arch_misc_flags() calling common_misc_flags()
twice. It is in fact worse, because afaict all of
perf_arch_guest_misc_flags() is 'common'.

Isn't the below more or less what you want?

static unsigned long misc_flags(struct pt_regs *regs)
{
	unsigned long flags = 0;

	if (regs->flags & PERF_EFLAGS_EXACT)
		flags |= PERF_RECORD_MISC_EXACT_IP;

	return flags;
}

static unsigned long native_flags(struct pt_regs *regs)
{
	unsigned long flags = 0;

	if (user_mode(regs))
		flags |= PERF_RECORD_MISC_USER;
	else
		flags |= PERF_RECORD_MISC_KERNEL;

	return flags;
}

static unsigned long guest_flags(struct pt_regs *regs)
{
	unsigned long guest_state = perf_guest_state();
	unsigned long flags = 0;

	if (guest_state & PERF_GUEST_ACTIVE) {
		if (guest_state & PERF_GUEST_USER)
			flags |= PERF_RECORD_MISC_GUEST_USER;
		else
			flags |= PERF_RECORD_MISC_GUEST_KERNEL;
	}

	return flags;
}

unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
{
	unsigned long flags;

	flags = misc_flags(regs);
	flags |= guest_flags(regs);

	return flags;
}

unsigned long perf_arch_misc_flags(struct pt_regs *regs)
{
	unsigned long flags;
	unsigned long guest;

	flags = misc_flags(regs);
	guest = guest_flags(regs);
	if (guest)
		flags |= guest;
	else
		flags |= native_flags(regs);

	return flags;
}

Note how both perf_arch*() functions end up calling both misc and guest.
Peter Zijlstra Nov. 8, 2024, 7:32 p.m. UTC | #4 
On Fri, Nov 08, 2024 at 08:20:44PM +0100, Peter Zijlstra wrote:

> Isn't the below more or less what you want?
> 
> static unsigned long misc_flags(struct pt_regs *regs)
> {
> 	unsigned long flags = 0;
> 
> 	if (regs->flags & PERF_EFLAGS_EXACT)
> 		flags |= PERF_RECORD_MISC_EXACT_IP;
> 
> 	return flags;
> }
> 
> static unsigned long native_flags(struct pt_regs *regs)
> {
> 	unsigned long flags = 0;
> 
> 	if (user_mode(regs))
> 		flags |= PERF_RECORD_MISC_USER;
> 	else
> 		flags |= PERF_RECORD_MISC_KERNEL;
> 
> 	return flags;
> }
> 
> static unsigned long guest_flags(struct pt_regs *regs)
> {
> 	unsigned long guest_state = perf_guest_state();
> 	unsigned long flags = 0;
> 
> 	if (guest_state & PERF_GUEST_ACTIVE) {
> 		if (guest_state & PERF_GUEST_USER)
> 			flags |= PERF_RECORD_MISC_GUEST_USER;
> 		else
> 			flags |= PERF_RECORD_MISC_GUEST_KERNEL;
> 	}
> 
> 	return flags;
> }
> 
> unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
> {
> 	unsigned long flags;
> 
> 	flags = misc_flags(regs);
> 	flags |= guest_flags(regs);
> 
> 	return flags;
> }
> 
> unsigned long perf_arch_misc_flags(struct pt_regs *regs)
> {
> 	unsigned long flags;
> 	unsigned long guest;
> 
> 	flags = misc_flags(regs);
> 	guest = guest_flags(regs);
> 	if (guest)
> 		flags |= guest;
> 	else
> 		flags |= native_flags(regs);
> 
> 	return flags;
> }

This last can be written more concise:

unsigned long perf_arch_misc_flags(struct pt_regs *regs)
{
	unsigned long flags;

	flags = guest_flags(regs);
	if (!flags)
		flags |= native_flags(regs);

	flgs |= misc_flags(regs);

	return flags;
}
diff mbox series

Patch

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index d19e939f3998..9fdc5fa22c66 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -3011,16 +3011,35 @@  unsigned long perf_arch_instruction_pointer(struct pt_regs *regs)
 	return regs->ip + code_segment_base(regs);
 }
 
+static unsigned long common_misc_flags(struct pt_regs *regs)
+{
+	if (regs->flags & PERF_EFLAGS_EXACT)
+		return PERF_RECORD_MISC_EXACT_IP;
+
+	return 0;
+}
+
+unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs)
+{
+	unsigned long guest_state = perf_guest_state();
+	unsigned long flags = common_misc_flags(regs);
+
+	if (!(guest_state & PERF_GUEST_ACTIVE))
+		return flags;
+
+	if (guest_state & PERF_GUEST_USER)
+		return flags & PERF_RECORD_MISC_GUEST_USER;
+	else
+		return flags & PERF_RECORD_MISC_GUEST_KERNEL;
+}
+
 unsigned long perf_arch_misc_flags(struct pt_regs *regs)
 {
 	unsigned int guest_state = perf_guest_state();
-	int misc = 0;
+	unsigned long misc = common_misc_flags(regs);
 
 	if (guest_state) {
-		if (guest_state & PERF_GUEST_USER)
-			misc |= PERF_RECORD_MISC_GUEST_USER;
-		else
-			misc |= PERF_RECORD_MISC_GUEST_KERNEL;
+		misc |= perf_arch_guest_misc_flags(regs);
 	} else {
 		if (user_mode(regs))
 			misc |= PERF_RECORD_MISC_USER;
@@ -3028,9 +3047,6 @@  unsigned long perf_arch_misc_flags(struct pt_regs *regs)
 			misc |= PERF_RECORD_MISC_KERNEL;
 	}
 
-	if (regs->flags & PERF_EFLAGS_EXACT)
-		misc |= PERF_RECORD_MISC_EXACT_IP;
-
 	return misc;
 }
 
diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
index feb87bf3d2e9..d95f902acc52 100644
--- a/arch/x86/include/asm/perf_event.h
+++ b/arch/x86/include/asm/perf_event.h
@@ -538,7 +538,9 @@  struct x86_perf_regs {
 
 extern unsigned long perf_arch_instruction_pointer(struct pt_regs *regs);
 extern unsigned long perf_arch_misc_flags(struct pt_regs *regs);
+extern unsigned long perf_arch_guest_misc_flags(struct pt_regs *regs);
 #define perf_arch_misc_flags(regs)	perf_arch_misc_flags(regs)
+#define perf_arch_guest_misc_flags(regs)	perf_arch_guest_misc_flags(regs)
 
 #include <asm/stacktrace.h>