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Message-ID: <163724608276.11128.6984852140789361165.tip-bot2@tip-bot2>
Date: Thu, 18 Nov 2021 14:34:42 -0000
From: "tip-bot2 for Sean Christopherson" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: perf/core] perf/core: Use static_call to optimize
perf_guest_info_callbacks
The following commit has been merged into the perf/core branch of tip:
Commit-ID: 87b940a0675e25261f022ac3e53e0dfff9cdb995
Gitweb: https://git.kernel.org/tip/87b940a0675e25261f022ac3e53e0dfff9cdb995
Author: Sean Christopherson <seanjc@...gle.com>
AuthorDate: Thu, 11 Nov 2021 02:07:30
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 17 Nov 2021 14:49:09 +01:00
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: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
Link: https://lore.kernel.org/r/20211111020738.2512932-10-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 ea47ef6..0ac7d86 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 5a3502c..3b3297a 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);
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