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From: Joel Fernandes <joel@joelfernandes.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Gustavo A. R. Silva" <gustavo@embeddedor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	paulmck <paulmck@kernel.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Andy Lutomirski <luto@kernel.org>,
	Tony Luck <tony.luck@intel.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	dan carpenter <dan.carpenter@oracle.com>,
	Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH v4 16/27] tracing: Remove regular RCU context for _rcuidle tracepoints (again)
Date: Fri, 6 Mar 2020 14:14:10 -0500	[thread overview]
Message-ID: <20200306191410.GB60713@google.com> (raw)
In-Reply-To: <20200306135925.50c38bec@gandalf.local.home>

On Fri, Mar 06, 2020 at 01:59:25PM -0500, Steven Rostedt wrote:
[snip]
> > > -			rcu_irq_enter_irqson();				\
> > > -		}							\
> > >  									\
> > >  		it_func_ptr = rcu_dereference_raw((tp)->funcs);		\
> > >  									\
> > >  		if (it_func_ptr) {					\
> > >  			do {						\
> > > +				int rcu_flags;				\
> > >  				it_func = (it_func_ptr)->func;		\
> > > +				if (rcuidle &&				\
> > > +				    (it_func_ptr)->requires_rcu)	\
> > > +					rcu_flags = trace_rcu_enter();	\
> > >  				__data = (it_func_ptr)->data;		\
> > >  				((void(*)(proto))(it_func))(args);	\
> > > +				if (rcuidle &&				\
> > > +				    (it_func_ptr)->requires_rcu)	\
> > > +					trace_rcu_exit(rcu_flags);	\  
> > 
> > Nit: If we have incurred the cost of trace_rcu_enter() once, we can call
> > it only once and then call trace_rcu_exit() after the do-while loop. That way
> > we pay the price only once.
> >
> 
> I thought about that, but the common case is only one callback attached at
> a time. To make the code complex for the non common case seemed too much
> of an overkill. If we find that it does help, it's best to do that as a
> separate patch because then if something goes wrong we know where it
> happened.
> 
> Currently, this provides the same overhead as if each callback did it
> themselves like we were proposing (but without the added need to do it for
> all instances of the callback).

That's ok, it could be a separate patch.

thanks,

 - Joel


  reply	other threads:[~2020-03-06 19:14 UTC|newest]

Thread overview: 84+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-21 13:34 [PATCH v4 00/27] tracing vs world Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 01/27] lockdep: Teach lockdep about "USED" <- "IN-NMI" inversions Peter Zijlstra
2020-02-21 15:08   ` Steven Rostedt
2020-02-21 20:25     ` Peter Zijlstra
2020-02-21 20:28       ` Steven Rostedt
2020-02-21 22:01       ` Frederic Weisbecker
2020-02-22  3:08   ` Joel Fernandes
2020-02-24 10:10     ` Peter Zijlstra
2020-02-25  2:12       ` Joel Fernandes
2020-03-20 12:58   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 02/27] hardirq/nmi: Allow nested nmi_enter() Peter Zijlstra
2020-02-21 22:21   ` Frederic Weisbecker
2020-02-24 12:13     ` Petr Mladek
2020-02-25  1:30       ` Frederic Weisbecker
2020-02-24 16:13     ` Peter Zijlstra
2020-02-25  3:09       ` Frederic Weisbecker
2020-02-25 15:41         ` Peter Zijlstra
2020-02-25 16:21           ` Frederic Weisbecker
2020-02-25 22:10           ` Frederic Weisbecker
2020-02-27  9:10             ` Peter Zijlstra
2020-02-27 13:34               ` Frederic Weisbecker
2020-02-21 13:34 ` [PATCH v4 03/27] x86/entry: Flip _TIF_SIGPENDING and _TIF_NOTIFY_RESUME handling Peter Zijlstra
2020-02-21 16:14   ` Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 04/27] x86/mce: Delete ist_begin_non_atomic() Peter Zijlstra
2020-02-21 19:07   ` Andy Lutomirski
2020-02-21 23:40   ` Frederic Weisbecker
2020-02-21 13:34 ` [PATCH v4 05/27] x86: Replace ist_enter() with nmi_enter() Peter Zijlstra
2020-02-21 19:05   ` Andy Lutomirski
2020-02-21 20:22     ` Peter Zijlstra
2020-02-24 10:43       ` Peter Zijlstra
2020-02-24 16:27         ` Steven Rostedt
2020-02-24 16:34           ` Peter Zijlstra
2020-02-24 16:47             ` Steven Rostedt
2020-02-24 21:31               ` Peter Zijlstra
2020-02-24 22:02                 ` Steven Rostedt
2020-02-26 10:25                   ` Peter Zijlstra
2020-02-26 13:16                     ` Peter Zijlstra
2020-02-26 10:27                   ` Peter Zijlstra
2020-02-26 15:20                     ` Steven Rostedt
2020-03-07  1:53                     ` Masami Hiramatsu
2020-02-21 13:34 ` [PATCH v4 06/27] x86/doublefault: Remove memmove() call Peter Zijlstra
2020-02-21 19:10   ` Andy Lutomirski
2020-02-21 13:34 ` [PATCH v4 07/27] rcu: Make RCU IRQ enter/exit functions rely on in_nmi() Peter Zijlstra
2020-02-26  0:23   ` Frederic Weisbecker
2020-02-21 13:34 ` [PATCH v4 08/27] rcu/kprobes: Comment why rcu_nmi_enter() is marked NOKPROBE Peter Zijlstra
2020-02-26  0:27   ` Frederic Weisbecker
2020-02-21 13:34 ` [PATCH v4 09/27] rcu: Rename rcu_irq_{enter,exit}_irqson() Peter Zijlstra
2020-02-21 20:21   ` Steven Rostedt
2020-02-24 10:24     ` Peter Zijlstra
2020-02-26  0:35   ` Frederic Weisbecker
2020-02-21 13:34 ` [PATCH v4 10/27] rcu: Mark rcu_dynticks_curr_cpu_in_eqs() inline Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 11/27] rcu,tracing: Create trace_rcu_{enter,exit}() Peter Zijlstra
2020-03-06 11:50   ` Peter Zijlstra
2020-03-06 12:40     ` Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 12/27] sched,rcu,tracing: Avoid tracing before in_nmi() is correct Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 13/27] x86,tracing: Add comments to do_nmi() Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 14/27] perf,tracing: Prepare the perf-trace interface for RCU changes Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 15/27] tracing: Employ trace_rcu_{enter,exit}() Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 16/27] tracing: Remove regular RCU context for _rcuidle tracepoints (again) Peter Zijlstra
2020-03-06 10:43   ` Peter Zijlstra
2020-03-06 11:31     ` Peter Zijlstra
2020-03-06 15:51       ` Alexei Starovoitov
2020-03-06 16:04         ` Mathieu Desnoyers
2020-03-06 17:55           ` Steven Rostedt
2020-03-06 18:45             ` Joel Fernandes
2020-03-06 18:59               ` Steven Rostedt
2020-03-06 19:14                 ` Joel Fernandes [this message]
2020-03-06 20:22             ` Mathieu Desnoyers
2020-03-06 20:45               ` Steven Rostedt
2020-03-06 20:55                 ` Mathieu Desnoyers
2020-03-06 21:06                   ` Steven Rostedt
2020-03-06 23:10                   ` Alexei Starovoitov
2020-03-06 17:21         ` Joel Fernandes
2020-02-21 13:34 ` [PATCH v4 17/27] perf,tracing: Allow function tracing when !RCU Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 18/27] x86/int3: Ensure that poke_int3_handler() is not traced Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 19/27] locking/atomics, kcsan: Add KCSAN instrumentation Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 20/27] asm-generic/atomic: Use __always_inline for pure wrappers Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 21/27] asm-generic/atomic: Use __always_inline for fallback wrappers Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 22/27] compiler: Simple READ/WRITE_ONCE() implementations Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 23/27] locking/atomics: Flip fallbacks and instrumentation Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 24/27] x86/int3: Avoid atomic instrumentation Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 25/27] lib/bsearch: Provide __always_inline variant Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 26/27] x86/int3: Inline bsearch() Peter Zijlstra
2020-02-21 13:34 ` [PATCH v4 27/27] x86/int3: Ensure that poke_int3_handler() is not sanitized Peter Zijlstra

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