From: Joel Fernandes <joelaf@google.com>
To: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Namhyung Kim <namhyung@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-rt-users <linux-rt-users@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Tom Zanussi <tom.zanussi@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Boqun Feng <boqun.feng@gmail.com>, fweisbec <fweisbec@gmail.com>,
Randy Dunlap <rdunlap@infradead.org>,
kbuild test robot <fengguang.wu@intel.com>,
baohong liu <baohong.liu@intel.com>,
vedang patel <vedang.patel@intel.com>,
kernel-team <kernel-team@lge.com>
Subject: Re: [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can
Date: Tue, 24 Apr 2018 11:59:32 -0700 [thread overview]
Message-ID: <CAJWu+opC9pLxoiXq7QDRUDe6ouC4ij398bHCfnUwp+h7Y_ssDg@mail.gmail.com> (raw)
In-Reply-To: <20180424182623.GA1357@linux.vnet.ibm.com>
Hi Paul,
On Tue, Apr 24, 2018 at 11:26 AM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
> On Tue, Apr 24, 2018 at 11:23:02AM -0700, Paul E. McKenney wrote:
>> On Tue, Apr 24, 2018 at 10:26:58AM -0700, Paul E. McKenney wrote:
>> > On Tue, Apr 24, 2018 at 09:01:34AM -0700, Joel Fernandes wrote:
>> > > On Tue, Apr 24, 2018 at 8:56 AM, Paul E. McKenney
>> > > <paulmck@linux.vnet.ibm.com> wrote:
>> > > > On Mon, Apr 23, 2018 at 05:22:44PM -0400, Steven Rostedt wrote:
>> > > >> On Mon, 23 Apr 2018 13:12:21 -0400 (EDT)
>> > > >> Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
>> > > >>
>> > > >>
>> > > >> > I'm inclined to explicitly declare the tracepoints with their given
>> > > >> > synchronization method. Tracepoint probe callback functions for currently
>> > > >> > existing tracepoints expect to have preemption disabled when invoked.
>> > > >> > This assumption will not be true anymore for srcu-tracepoints.
>> > > >>
>> > > >> Actually, why not have a flag attached to the tracepoint_func that
>> > > >> states if it expects preemption to be enabled or not? If a
>> > > >> trace_##event##_srcu() is called, then simply disable preemption before
>> > > >> calling the callbacks for it. That way if a callback is fine for use
>> > > >> with srcu, then it would require calling
>> > > >>
>> > > >> register_trace_##event##_may_sleep();
>> > > >>
>> > > >> Then if someone uses this on a tracepoint where preemption is disabled,
>> > > >> we simply do not call it.
>> > > >
>> > > > One more stupid question... If we are having to trace so much stuff
>> > > > in the idle loop, are we perhaps grossly overstating the extent of that
>> > > > "idle" loop? For being called "idle", this code seems quite busy!
>> > >
>> > > ;-)
>> > > The performance hit I am observing is when running a heavy workload,
>> > > like hackbench or something like that. That's what I am trying to
>> > > correct.
>> > > By the way is there any limitation on using SRCU too early during
>> > > boot? I backported Mathieu's srcu tracepoint patches but the kernel
>> > > hangs pretty early in the boot. I register lockdep probes in
>> > > start_kernel. I am hoping that's not why.
>> > >
>> > > I could also have just screwed up the backporting... may be for my
>> > > testing, I will just replace the rcu API with the srcu instead of all
>> > > of Mathieu's new TRACE_EVENT macros for SRCU, since all I am trying to
>> > > do right now is measure the performance of my patches with SRCU.
>> >
>> > Gah, yes, there is an entry on my capacious todo list on making SRCU
>> > grace periods work during early boot and mid-boot. Let me see what
>> > I can do...
>>
>> OK, just need to verify that you are OK with call_srcu()'s callbacks
>> not being invoked until sometime during core_initcall() time. (If you
>> really do need them to be invoked before that, in theory it is possible,
>> but in practice it is weird, even for RCU.)
>
> Oh, and that early at boot, you will need to use DEFINE_SRCU() or
> DEFINE_STATIC_SRCU() rather than dynamic allocation and initialization.
>
> Thanx, Paul
>
Oh ok.
About call_rcu, calling it later may be an issue since we register the
probes in start_kernel, for the first probe call_rcu will be sched,
but for the second one I think it'll try to call_rcu to get rid of the
first one.
This is the relevant code that gets called when probes are added:
static inline void release_probes(struct tracepoint_func *old)
{
if (old) {
struct tp_probes *tp_probes = container_of(old,
struct tp_probes, probes[0]);
call_rcu_sched(&tp_probes->rcu, rcu_free_old_probes);
}
}
Maybe we can somehow defer the call_srcu until later? Would that be possible?
also Mathieu, you didn't modify the call_rcu_sched in your prototype
to be changed to use call_srcu, should you be doing that?
thanks,
- Joel
next prev parent reply other threads:[~2018-04-24 18:59 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-17 4:07 [RFC v4 0/4] Centralize and unify usage of preempt/irq tracepoints Joel Fernandes
2018-04-17 4:07 ` [RFC v4 1/4] tracepoint: Add API to not do lockdep checks during RCU ops Joel Fernandes
2018-04-17 4:07 ` [RFC v4 2/4] softirq: reorder trace_softirqs_on to prevent lockdep splat Joel Fernandes
2018-04-17 4:07 ` [RFC v4 3/4] irqflags: Avoid unnecessary calls to trace_ if you can Joel Fernandes
2018-04-18 9:02 ` Masami Hiramatsu
2018-04-19 5:43 ` Namhyung Kim
2018-04-20 7:07 ` Joel Fernandes
2018-04-23 1:14 ` Joel Fernandes
2018-04-23 3:19 ` Paul E. McKenney
2018-04-23 14:31 ` Mathieu Desnoyers
2018-04-23 14:53 ` Steven Rostedt
2018-04-23 14:59 ` Mathieu Desnoyers
2018-04-23 15:12 ` Paul E. McKenney
2018-04-23 16:18 ` Steven Rostedt
2018-04-23 17:12 ` Mathieu Desnoyers
2018-04-23 17:24 ` Joel Fernandes
2018-04-23 21:22 ` Steven Rostedt
2018-04-24 15:56 ` Paul E. McKenney
2018-04-24 16:01 ` Joel Fernandes
2018-04-24 17:26 ` Paul E. McKenney
2018-04-24 18:23 ` Paul E. McKenney
2018-04-24 18:26 ` Paul E. McKenney
2018-04-24 18:59 ` Joel Fernandes [this message]
2018-04-24 19:01 ` Joel Fernandes
2018-04-24 19:09 ` Paul E. McKenney
2018-04-24 19:16 ` Joel Fernandes
2018-04-24 23:21 ` Mathieu Desnoyers
2018-04-24 23:46 ` Joel Fernandes
2018-04-25 0:10 ` Paul E. McKenney
2018-04-25 4:20 ` Paul E. McKenney
2018-04-25 21:27 ` Joel Fernandes
2018-04-25 21:35 ` Paul E. McKenney
2018-04-25 21:40 ` Mathieu Desnoyers
2018-04-25 22:51 ` Steven Rostedt
2018-04-26 15:03 ` Mathieu Desnoyers
2018-04-26 16:08 ` Mathieu Desnoyers
2018-04-25 23:13 ` Joel Fernandes
2018-04-26 15:13 ` Mathieu Desnoyers
2018-04-26 15:20 ` Joel Fernandes
2018-04-26 15:49 ` Paul E. McKenney
2018-04-23 15:49 ` Joel Fernandes
2018-04-26 2:18 ` Joel Fernandes
2018-05-01 1:18 ` Joel Fernandes
2018-04-17 4:07 ` [RFC v4 4/4] tracing: Centralize preemptirq tracepoints and unify their usage Joel Fernandes
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