linux-kernel - Re: CFS review

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Date:	Thu, 2 Aug 2007 17:46:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Roman Zippel <zippel@...ux-m68k.org>
Cc:	Mike Galbraith <efault@....de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: CFS review


* Roman Zippel <zippel@...ux-m68k.org> wrote:

> [...] With the increased text comes increased runtime memory usage, 
> e.g. task_struct increased so that only 5 of them instead 6 fit now 
> into 8KB.

yeah, thanks for the reminder, this is on my todo list. As i suspect you 
noticed it too, much of the task_struct size increase is not fundamental 
and not related to 64-bit math at all - it's simply debug and 
instrumentation overhead.

Look at the following table (i386, nodebug):

                         size 
                         ----
    pre-CFS              1328
        CFS              1472
        CFS+patch        1376 

the very small patch below gets rid of 96 bytes. And that's only the
beginning.

	Ingo

-------------------------------------------------->
---
 include/linux/sched.h |   21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h
+++ linux/include/linux/sched.h
@@ -905,23 +905,28 @@ struct sched_entity {
 	struct rb_node		run_node;
 	unsigned int		on_rq;
 
+	u64			exec_start;
+	u64			sum_exec_runtime;
 	u64			wait_start_fair;
+	u64			sleep_start_fair;
+
+#ifdef CONFIG_SCHEDSTATS
 	u64			wait_start;
-	u64			exec_start;
+	u64			wait_max;
+	s64			sum_wait_runtime;
+
 	u64			sleep_start;
-	u64			sleep_start_fair;
-	u64			block_start;
 	u64			sleep_max;
+	s64			sum_sleep_runtime;
+
+	u64			block_start;
 	u64			block_max;
 	u64			exec_max;
-	u64			wait_max;
-	u64			last_ran;
 
-	u64			sum_exec_runtime;
-	s64			sum_wait_runtime;
-	s64			sum_sleep_runtime;
 	unsigned long		wait_runtime_overruns;
 	unsigned long		wait_runtime_underruns;
+#endif
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	struct sched_entity	*parent;
 	/* rq on which this entity is (to be) queued: */
-
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