lkml.org 
[lkml]   [2021]   [Nov]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
Subject[PATCH v4 09/17] perf/core: Use static_call to optimize perf_guest_info_callbacks
From
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: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Like Xu <like.xu.linux@gmail.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
include/linux/perf_event.h | 34 ++++++++--------------------------
kernel/events/core.c | 15 +++++++++++++++
2 files changed, 23 insertions(+), 26 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index ea47ef616ee0..0ac7d867ca0c 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -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);
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1c8d341ecc77..b4fd928e4ff8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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);
--
2.34.0.rc0.344.g81b53c2807-goog
\
 
 \ /
  Last update: 2021-11-11 03:09    [W:0.212 / U:0.608 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site