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7675104990
This is useful for locking primitives that can effect multiple wakeups per operation and want to avoid lock internal lock contention by delaying the wakeups until we've released the lock internal locks. Alternatively it can be used to avoid issuing multiple wakeups, and thus save a few cycles, in packet processing. Queue all target tasks and wakeup once you've processed all packets. That way you avoid waking the target task multiple times if there were multiple packets for the same task. Properties of a wake_q are: - Lockless, as queue head must reside on the stack. - Being a queue, maintains wakeup order passed by the callers. This can be important for otherwise, in scenarios where highly contended locks could affect any reliance on lock fairness. - A queued task cannot be added again until it is woken up. This patch adds the needed infrastructure into the scheduler code and uses the new wake_list to delay the futex wakeups until after we've released the hash bucket locks. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> [tweaks, adjustments, comments, etc.] Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Chris Mason <clm@fb.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: George Spelvin <linux@horizon.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Manfred Spraul <manfred@colorfullife.com> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Link: http://lkml.kernel.org/r/1430494072-30283-2-git-send-email-dave@stgolabs.net Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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