Ingo, I tested this one, and I think it makes sense in any case as an optimization. It should also be good for -stable kernels.
Does it look OK? Thanks, Miklos ---- From: Miklos Szeredi <mszer...@suse.cz> This patch fixes bug #12208: http://bugzilla.kernel.org/show_bug.cgi?id=12208 Don't preempt tasks in preempt_schedule() if they are already in the process of going to sleep. Otherwise the task would wake up only to go to sleep again. Due to the way wait_task_inactive() works this can also drastically slow down ptrace: - task A is ptracing task B - task B stops on a trace event - task A is woken up and preempts task B - task A calls ptrace on task B, which does ptrace_check_attach() - this calls wait_task_inactive(), which sees that task B is still on the runq - task A goes to sleep for a jiffy - ... Since UML does lots of the above sequences, those jiffies quickly add up to make it slow as hell. Signed-off-by: Miklos Szeredi <mszer...@suse.cz> CC: sta...@kernel.org --- kernel/sched.c | 4 ++++ 1 file changed, 4 insertions(+) Index: linux.git/kernel/sched.c =================================================================== --- linux.git.orig/kernel/sched.c 2009-03-20 09:40:47.000000000 +0100 +++ linux.git/kernel/sched.c 2009-03-20 10:28:56.000000000 +0100 @@ -4632,6 +4632,10 @@ asmlinkage void __sched preempt_schedule if (likely(ti->preempt_count || irqs_disabled())) return; + /* No point in preempting we are just about to go to sleep. */ + if (current->state != TASK_RUNNING) + return; + do { add_preempt_count(PREEMPT_ACTIVE); schedule(); ------------------------------------------------------------------------------ Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are powering Web 2.0 with engaging, cross-platform capabilities. Quickly and easily build your RIAs with Flex Builder, the Eclipse(TM)based development software that enables intelligent coding and step-through debugging. Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
