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


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