From c96d145e71c5c84601322d85748512e09d7b325f Mon Sep 17 00:00:00 2001 From: "Chen, Kenneth W" Date: Tue, 27 Jun 2006 02:54:28 -0700 Subject: [PATCH] [PATCH] sched: fix smt nice lock contention and optimization Initial report and lock contention fix from Chris Mason: Recent benchmarks showed some performance regressions between 2.6.16 and 2.6.5. We tracked down one of the regressions to lock contention in schedule heavy workloads (~70,000 context switches per second) kernel/sched.c:dependent_sleeper() was responsible for most of the lock contention, hammering on the run queue locks. The patch below is more of a discussion point than a suggested fix (although it does reduce lock contention significantly). The dependent_sleeper code looks very expensive to me, especially for using a spinlock to bounce control between two different siblings in the same cpu. It is further optimized: * perform dependent_sleeper check after next task is determined * convert wake_sleeping_dependent to use trylock * skip smt runqueue check if trylock fails * optimize double_rq_lock now that smt nice is converted to trylock * early exit in searching first SD_SHARE_CPUPOWER domain * speedup fast path of dependent_sleeper [akpm@osdl.org: cleanup] Signed-off-by: Ken Chen Acked-by: Ingo Molnar Acked-by: Con Kolivas Signed-off-by: Nick Piggin Acked-by: Chris Mason Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-format-patch failed