From: Oleg Nesterov <oleg@redhat.com>
To: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Namhyung Kim <namhyung.kim@lge.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@redhat.com>,
linux-kernel@vger.kernel.org,
Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [RFC PATCH 0/2] tracing: Teach FETCH_MTD_symbol to handle per-cpu data
Date: Wed, 27 Nov 2013 18:41:17 +0100 [thread overview]
Message-ID: <20131127174117.GC26138@redhat.com> (raw)
In-Reply-To: <5295C304.1050702@hitachi.com>
On 11/27, Masami Hiramatsu wrote:
>
> (2013/11/27 2:43), Oleg Nesterov wrote:
> >
> > This doesn't allow to read the data from other CPUs, but at least
> > the changes are simple and this_cpu_ is better than the reading
> > from the obviously wrong address.
>
> Yeah, usually per_cpu variable is used in current cpu context.
>
> >> For the dynamic allocated per-cpu things, it is also good to give
> >> a straight operation, like +10(percpu(%rdi)).
> >
> > Probably yes, but this needs more changes and I am still not sure
> > this is really useful. And if we do this, we probably also need
> > to allow to read from other CPUs...
>
> No, it is enough to provide "percpu(FETCHARG)" which just returns
> current cpu's percpu variable address.
I don't really agree. I am not saying this is terribly useful, but:
> (Note that kprobes handler
> runs in interrupt)
but this doesn't matter at all, I think. The code can execute, say,
__percpu_counter_sum-like code.
And even if we dump the .data..percpu memory (@percpu_symbol) the
user might want to know the "global" state of this per-cpu object.
And note that sometimes DEFINE_PER_CPU doesn't really connect to
smp_processor_id(). Just for example, bp_cpuinfo[]. It is never
used as this-cpu-data. This means that @bp_cpuinfo+whatever is
always pointless.
But anyway I agree, this is not that important, lets ignore.
Oleg.
next prev parent reply other threads:[~2013-11-27 17:40 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-23 20:15 [PATCH 0/1] tracing: Introduce "pseudo registers" for FETCH_MTD_reg Oleg Nesterov
2013-11-23 20:16 ` [PATCH 1/1] " Oleg Nesterov
2013-11-24 7:32 ` Masami Hiramatsu
2013-11-25 8:04 ` Namhyung Kim
2013-11-25 14:35 ` Oleg Nesterov
2013-11-25 17:21 ` [RFC PATCH 0/3] tracing: Teach FETCH_MTD_{symbol,deref} to handle per-cpu data Oleg Nesterov
2013-11-25 17:21 ` [RFC PATCH 1/3] tracing: Don't mangle sc->addr in update_symbol_cache() Oleg Nesterov
2013-11-25 17:21 ` [RFC PATCH 2/3] tracing: introduce {calc,parse}_probe_offset() for FETCH_MTD_{symbol,deref} Oleg Nesterov
2013-11-25 17:22 ` [RFC PATCH 3/3] tracing: Teach FETCH_MTD_{symbol,deref} to handle per-cpu data Oleg Nesterov
2013-11-26 9:34 ` Masami Hiramatsu
2013-11-26 17:43 ` [RFC PATCH 0/2] tracing: Teach FETCH_MTD_symbol " Oleg Nesterov
2013-11-26 17:44 ` [RFC PATCH 1/2] tracing: Don't update sc->addr in update_symbol_cache() Oleg Nesterov
2013-11-26 17:44 ` [RFC PATCH 2/2] tracing: Teach FETCH_MTD_symbol to handle per-cpu data Oleg Nesterov
2013-11-26 17:50 ` modules, add_kallsyms() && DEFINE_PER_CPU Oleg Nesterov
2013-11-27 2:23 ` Masami Hiramatsu
2013-11-27 8:20 ` Namhyung Kim
2013-11-27 11:22 ` Masami Hiramatsu
2013-11-27 13:35 ` Oleg Nesterov
2013-11-28 2:02 ` Masami Hiramatsu
2013-11-27 11:30 ` [RFC PATCH 2/2] tracing: Teach FETCH_MTD_symbol to handle per-cpu data Masami Hiramatsu
2013-11-27 0:37 ` [RFC PATCH 0/2] " Namhyung Kim
2013-11-27 10:01 ` Masami Hiramatsu
2013-11-27 17:41 ` Oleg Nesterov [this message]
2013-11-28 2:55 ` Masami Hiramatsu
2013-11-25 19:29 ` [PATCH 0/2] tracing: Add $cpu and $current probe-vars Oleg Nesterov
2013-11-25 19:29 ` [PATCH 1/2] " Oleg Nesterov
2013-11-26 2:21 ` Masami Hiramatsu
2013-11-26 17:23 ` Oleg Nesterov
2013-11-27 8:22 ` Masami Hiramatsu
2013-11-27 17:05 ` Oleg Nesterov
2013-11-28 2:51 ` Masami Hiramatsu
2013-11-25 19:30 ` [PATCH 2/2] tracing: Kill FETCH_MTD_retval, reimplement $retval via pseudo_reg_retval() Oleg Nesterov
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