linux-kernel - [PATCH v2 06/28] locking/rwlocks: Add contention detection for rwlocks

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Date:   Tue,  2 Feb 2021 10:57:12 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Ben Gardon <bgardon@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Davidlohr Bueso <dbueso@...e.de>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v2 06/28] locking/rwlocks: Add contention detection for rwlocks

rwlocks do not currently have any facility to detect contention
like spinlocks do. In order to allow users of rwlocks to better manage
latency, add contention detection for queued rwlocks.

CC: Ingo Molnar <mingo@...hat.com>
CC: Will Deacon <will@...nel.org>
Acked-by: Peter Zijlstra <peterz@...radead.org>
Acked-by: Davidlohr Bueso <dbueso@...e.de>
Acked-by: Waiman Long <longman@...hat.com>
Acked-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Ben Gardon <bgardon@...gle.com>
---
 include/asm-generic/qrwlock.h | 24 ++++++++++++++++++------
 include/linux/rwlock.h        |  7 +++++++
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h
index 84ce841ce735..0020d3b820a7 100644
--- a/include/asm-generic/qrwlock.h
+++ b/include/asm-generic/qrwlock.h
@@ -14,6 +14,7 @@
 #include <asm/processor.h>
 
 #include <asm-generic/qrwlock_types.h>
+#include <asm-generic/qspinlock.h>
 
 /*
  * Writer states & reader shift and bias.
@@ -116,15 +117,26 @@ static inline void queued_write_unlock(struct qrwlock *lock)
 	smp_store_release(&lock->wlocked, 0);
 }
 
+/**
+ * queued_rwlock_is_contended - check if the lock is contended
+ * @lock : Pointer to queue rwlock structure
+ * Return: 1 if lock contended, 0 otherwise
+ */
+static inline int queued_rwlock_is_contended(struct qrwlock *lock)
+{
+	return arch_spin_is_locked(&lock->wait_lock);
+}
+
 /*
  * Remapping rwlock architecture specific functions to the corresponding
  * queue rwlock functions.
  */
-#define arch_read_lock(l)	queued_read_lock(l)
-#define arch_write_lock(l)	queued_write_lock(l)
-#define arch_read_trylock(l)	queued_read_trylock(l)
-#define arch_write_trylock(l)	queued_write_trylock(l)
-#define arch_read_unlock(l)	queued_read_unlock(l)
-#define arch_write_unlock(l)	queued_write_unlock(l)
+#define arch_read_lock(l)		queued_read_lock(l)
+#define arch_write_lock(l)		queued_write_lock(l)
+#define arch_read_trylock(l)		queued_read_trylock(l)
+#define arch_write_trylock(l)		queued_write_trylock(l)
+#define arch_read_unlock(l)		queued_read_unlock(l)
+#define arch_write_unlock(l)		queued_write_unlock(l)
+#define arch_rwlock_is_contended(l)	queued_rwlock_is_contended(l)
 
 #endif /* __ASM_GENERIC_QRWLOCK_H */
diff --git a/include/linux/rwlock.h b/include/linux/rwlock.h
index 3dcd617e65ae..7ce9a51ae5c0 100644
--- a/include/linux/rwlock.h
+++ b/include/linux/rwlock.h
@@ -128,4 +128,11 @@ do {								\
 	1 : ({ local_irq_restore(flags); 0; }); \
 })
 
+#ifdef arch_rwlock_is_contended
+#define rwlock_is_contended(lock) \
+	 arch_rwlock_is_contended(&(lock)->raw_lock)
+#else
+#define rwlock_is_contended(lock)	((void)(lock), 0)
+#endif /* arch_rwlock_is_contended */
+
 #endif /* __LINUX_RWLOCK_H */
-- 
2.30.0.365.g02bc693789-goog