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

Mathieu Desnoyers
2008-03-28T11:38:18Z

* Ingo Molnar (mingo@elte.hu) wrote:
>
> * 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.
>

Hrm, you are only quoting my introduction, where I introduce the reason
why I do in a more in-depth analysis on a _single_ ftrace statement.

Ingo, if you care to read the rest of my email, you will discover that I
concentrated my effort on a single ftrace statement in context_switch().
Whether or not I removed the trace points from kernel/sched_fair.c does
not change the validity of the results that follow. I commented out your
ad-hoc tracepoints from sched.c by hand in my test cases, and
sched_fair.c trace points were there in every scenario, so they were
invariant and _not_ considered, except in this introduction you quoted.

Mathieu

> 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;
>
> /*

--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68