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| author |   Waiman Long <Waiman.Long@hp.com> | 2015-06-19 11:50:01 -0400 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2015-07-06 14:11:28 +0200 |
| commit | 0e06e5be70d392aa842c1455ec2d0baf62aeed48 (patch) | |
| tree | c4974970b68768690e0516927b51a7b3c8800014 /include/asm-generic/qrwlock.h | |
| parent | locking/qrwlock: Rename functions to queued_*() (diff) | |
| download | wireguard-linux-0e06e5be70d392aa842c1455ec2d0baf62aeed48.tar.xz wireguard-linux-0e06e5be70d392aa842c1455ec2d0baf62aeed48.zip | |
locking/qrwlock: Better optimization for interrupt context readers
The qrwlock is fair in the process context, but becoming unfair when
in the interrupt context to support use cases like the tasklist_lock.
The current code isn't that well-documented on what happens when
in the interrupt context. The rspin_until_writer_unlock() will only
spin if the writer has gotten the lock. If the writer is still in the
waiting state, the increment in the reader count will cause the writer
to remain in the waiting state and the new interrupt context reader
will get the lock and return immediately. The current code, however,
does an additional read of the lock value which is not necessary as
the information has already been there in the fast path. This may
sometime cause an additional cacheline transfer when the lock is
highly contended.
This patch passes the lock value information gotten in the fast path
to the slow path to eliminate the additional read. It also documents
the action for the interrupt context readers more clearly.
Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1434729002-57724-3-git-send-email-Waiman.Long@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/asm-generic/qrwlock.h')
| -rw-r--r-- | include/asm-generic/qrwlock.h | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h index 55e3ee1d2415..deb9e8b0eb9e 100644 --- a/include/asm-generic/qrwlock.h +++ b/include/asm-generic/qrwlock.h @@ -36,7 +36,7 @@ /* * External function declarations */ -extern void queued_read_lock_slowpath(struct qrwlock *lock); +extern void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts); extern void queued_write_lock_slowpath(struct qrwlock *lock); /** @@ -105,7 +105,7 @@ static inline void queued_read_lock(struct qrwlock *lock) return; /* The slowpath will decrement the reader count, if necessary. */ - queued_read_lock_slowpath(lock); + queued_read_lock_slowpath(lock, cnts); } /** |