Re: [patch for 2.6.26 0/7] Architecture Independent Markers

Ingo Molnar
2008-03-28T09:43:55Z

* Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:

> Let's compare one marker against one ftrace statement in sched.o on
> the sched-dev tree on x86_32 and see where your "bloat" impression
> about markers comes from. I think it's mostly due to the different
> metrics we use.
>
> sched.o w/o CONFIG_CONTEXT_SWITCH_TRACER
> text data bss dec hex filename
> 46564 2924 200 49688 c218 kernel/sched.o
>
> Let's get an idea of CONFIG_CONTEXT_SWITCH_TRACER impact on sched.o :
>
> sched.o with CONFIG_CONTEXT_SWITCH_TRACER
>
> text data bss dec hex filename
> 46788 2924 200 49912 c2f8 kernel/sched.o
>
> 224 bytes added for 6 ftrace_*(). This is partly due to the helper function
> ftrace_all_fair_tasks(). So let's be fair and not take it in account.

it's not 6 ftrace calls, you forgot about kernel/sched_fair.c, so it's 9
tracepoints.

note that all but the 2 core trace hooks are temporary, i used them to
debug a specific scheduler problem. Especially one trace point:
ftrace_all_fair_tasks() is a totally ad-hoc trace-all-tasks-in-the-rq
heavy function.

if you want to compare apples to apples, try the patch below, which
removes the ad-hoc tracepoints.

Ingo

------------------------>
Subject: no: ad hoc ftrace points
From: Ingo Molnar <mingo@elte.hu>
Date: Fri Mar 28 10:30:37 CET 2008

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/sched.c | 47 -----------------------------------------------
kernel/sched_fair.c | 3 ---
2 files changed, 50 deletions(-)

Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -2005,53 +2005,6 @@ static int sched_balance_self(int cpu, i

#endif /* CONFIG_SMP */

-#ifdef CONFIG_CONTEXT_SWITCH_TRACER
-
-void ftrace_task(struct task_struct *p, void *__tr, void *__data)
-{
-#if 0
- /*
- * trace timeline tree
- */
- __trace_special(__tr, __data,
- p->pid, p->se.vruntime, p->se.sum_exec_runtime);
-#else
- /*
- * trace balance metrics
- */
- __trace_special(__tr, __data,
- p->pid, p->se.avg_overlap, 0);
-#endif
-}
-
-void ftrace_all_fair_tasks(void *__rq, void *__tr, void *__data)
-{
- struct task_struct *p;
- struct sched_entity *se;
- struct rb_node *curr;
- struct rq *rq = __rq;
-
- if (rq->cfs.curr) {
- p = task_of(rq->cfs.curr);
- ftrace_task(p, __tr, __data);
- }
- if (rq->cfs.next) {
- p = task_of(rq->cfs.next);
- ftrace_task(p, __tr, __data);
- }
-
- for (curr = first_fair(&rq->cfs); curr; curr = rb_next(curr)) {
- se = rb_entry(curr, struct sched_entity, run_node);
- if (!entity_is_task(se))
- continue;
-
- p = task_of(se);
- ftrace_task(p, __tr, __data);
- }
-}
-
-#endif
-
/***
* try_to_wake_up - wake up a thread
* @p: the to-be-woken-up thread
Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -991,8 +991,6 @@ wake_affine(struct rq *rq, struct sched_
if (!(this_sd->flags & SD_WAKE_AFFINE))
return 0;

- ftrace_special(__LINE__, curr->se.avg_overlap, sync);
- ftrace_special(__LINE__, p->se.avg_overlap, -1);
/*
* If the currently running task will sleep within
* a reasonable amount of time then attract this newly
@@ -1118,7 +1116,6 @@ static void check_preempt_wakeup(struct
if (unlikely(se == pse))
return;

- ftrace_special(__LINE__, p->pid, se->last_wakeup);
cfs_rq_of(pse)->next = pse;

/*