[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-Id: <E1LkbGe-00039U-Hc@pomaz-ex.szeredi.hu>
Date: Fri, 20 Mar 2009 10:43:56 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: mingo@...e.hu
Cc: peterz@...radead.org, roland@...hat.com, efault@....de,
rjw@...k.pl, jdike@...toit.com,
user-mode-linux-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
akpm@...ux-foundation.org
Subject: [patch] don't preempt not TASK_RUNNING tasks
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 <mszeredi@...e.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 <mszeredi@...e.cz>
CC: stable@...nel.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();
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists