Commit 87b940a0 authored by Sean Christopherson's avatar Sean Christopherson Committed by Peter Zijlstra
Browse files

perf/core: Use static_call to optimize perf_guest_info_callbacks 



Use static_call to optimize perf's guest callbacks on arm64 and x86,
which are now the only architectures that define the callbacks.  Use
DEFINE_STATIC_CALL_RET0 as the default/NULL for all guest callbacks, as
the callback semantics are that a return value '0' means "not in guest".

static_call obviously avoids the overhead of CONFIG_RETPOLINE=y, but is
also advantageous versus other solutions, e.g. per-cpu callbacks, in that
a per-cpu memory load is not needed to detect the !guest case.

Based on code from Peter and Like.

Suggested-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20211111020738.2512932-10-seanjc@google.com
parent 2aef6f30

include/linux/perf_event.h

+8 −26
Original line number Diff line number Diff line
@@ -1244,40 +1244,22 @@ extern void perf_event_bpf_event(struct bpf_prog *prog, 


#ifdef CONFIG_GUEST_PERF_EVENTS

extern struct perf_guest_info_callbacks __rcu *perf_guest_cbs;

static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void)

{

	/*

	 * Callbacks are RCU-protected and must be READ_ONCE to avoid reloading

	 * the callbacks between a !NULL check and dereferences, to ensure

	 * pending stores/changes to the callback pointers are visible before a

	 * non-NULL perf_guest_cbs is visible to readers, and to prevent a

	 * module from unloading callbacks while readers are active.

	 */

	return rcu_dereference(perf_guest_cbs);

}



DECLARE_STATIC_CALL(__perf_guest_state, *perf_guest_cbs->state);

DECLARE_STATIC_CALL(__perf_guest_get_ip, *perf_guest_cbs->get_ip);

DECLARE_STATIC_CALL(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr);



static inline unsigned int perf_guest_state(void)

{

	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();



	return guest_cbs ? guest_cbs->state() : 0;

	return static_call(__perf_guest_state)();

}

static inline unsigned long perf_guest_get_ip(void)

{

	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();



	/*

	 * Arbitrarily return '0' in the unlikely scenario that the callbacks

	 * are unregistered between checking guest state and getting the IP.

	 */

	return guest_cbs ? guest_cbs->get_ip() : 0;

	return static_call(__perf_guest_get_ip)();

}

static inline unsigned int perf_guest_handle_intel_pt_intr(void)

{

	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();



	if (guest_cbs && guest_cbs->handle_intel_pt_intr)

		return guest_cbs->handle_intel_pt_intr();

	return 0;

	return static_call(__perf_guest_handle_intel_pt_intr)();

}

extern void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);

extern void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);

kernel/events/core.c

+15 −0
Original line number Diff line number Diff line
@@ -6524,12 +6524,23 @@ static void perf_pending_event(struct irq_work *entry) 
#ifdef CONFIG_GUEST_PERF_EVENTS

struct perf_guest_info_callbacks __rcu *perf_guest_cbs;



DEFINE_STATIC_CALL_RET0(__perf_guest_state, *perf_guest_cbs->state);

DEFINE_STATIC_CALL_RET0(__perf_guest_get_ip, *perf_guest_cbs->get_ip);

DEFINE_STATIC_CALL_RET0(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr);



void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)

{

	if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs)))

		return;



	rcu_assign_pointer(perf_guest_cbs, cbs);

	static_call_update(__perf_guest_state, cbs->state);

	static_call_update(__perf_guest_get_ip, cbs->get_ip);



	/* Implementing ->handle_intel_pt_intr is optional. */

	if (cbs->handle_intel_pt_intr)

		static_call_update(__perf_guest_handle_intel_pt_intr,

				   cbs->handle_intel_pt_intr);

}

EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
@@ -6539,6 +6550,10 @@ void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) 
		return;



	rcu_assign_pointer(perf_guest_cbs, NULL);

	static_call_update(__perf_guest_state, (void *)&__static_call_return0);

	static_call_update(__perf_guest_get_ip, (void *)&__static_call_return0);

	static_call_update(__perf_guest_handle_intel_pt_intr,

			   (void *)&__static_call_return0);

	synchronize_rcu();

}

EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);