From: Steven Rostedt <rostedt@goodmis.org>
To: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, x86@kernel.org,
Nadav Amit <nadav.amit@gmail.com>,
Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Song Liu <songliubraving@fb.com>,
Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH 3/3] x86/ftrace: Use text_poke()
Date: Fri, 4 Oct 2019 09:40:14 -0400 [thread overview]
Message-ID: <20191004094014.72a990ee@gandalf.local.home> (raw)
In-Reply-To: <7b4196a4-b6e1-7e55-c3e1-a02d97c262c7@redhat.com>
On Fri, 4 Oct 2019 10:10:47 +0200
Daniel Bristot de Oliveira <bristot@redhat.com> wrote:
> [ In addition ]
>
> Currently, ftrace_rec entries are ordered inside the group of functions, but
> "groups of function" are not ordered. So, the current int3 handler does a (*):
>
> for_each_group_of_functions:
> check if the ip is in the range ----> n by the number of groups.
> do a bsearch. ----> log(n) by the numbers of entry
> in the group.
>
> If, instead, it uses an ordered vector, the complexity would be log(n) by the
> total number of entries, which is better. So, how bad is the idea of:
BTW, I'm currently rewriting the grouping of the vectors, in order to
shrink the size of each dyn_ftrace_rec (as we discussed at Kernel
Recipes). I can make the groups all sorted in doing so, thus we can
load the sorted if that's needed, without doing anything special.
>
> in the enabling ftrace code path, it:
> discover the number of entries
> alloc a buffer
> discover the order of the groups
> for each group in the correct order
> queue the entry in the buffer
> apply the changes using the text_poke...
>
> In this way we would optimize the two hot-paths:
> int3 will be log(n)
> IPIs bounded to 3.
>
> I am not saying we need to do it now, as Steve said, not sure if this is a big
> problem, but... those that don't like kernel interference may complain. But if
> we leave the per-use-case vector in the text_poke_batch interface, things will
> be easier to fix.
>
> NOTE: the other IPIs are generated by hooking the tracepoints and switching the
> code to RO/RW...
Yeah, I did a trace of who is doing the on_each_cpu() call, and saw it
coming from the RO/RW changes, which this patch series removes.
-- Steve
>
> * as far as I understood ftrace_location_range().
>
> -- Daniel
>
> > -- Steve
> >
next prev parent reply other threads:[~2019-10-04 13:40 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-27 18:06 [PATCH 0/3] Rewrite x86/ftrace to use text_poke() Peter Zijlstra
2019-08-27 18:06 ` [PATCH 1/3] x86/alternatives: Teach text_poke_bp() to emulate instructions Peter Zijlstra
2019-10-03 5:00 ` Masami Hiramatsu
2019-10-03 8:27 ` Peter Zijlstra
2019-10-03 11:01 ` Peter Zijlstra
2019-10-03 12:32 ` Peter Zijlstra
2019-10-04 13:45 ` Masami Hiramatsu
2019-10-07 8:05 ` Peter Zijlstra
2019-10-09 13:07 ` x86/kprobes bug? (was: [PATCH 1/3] x86/alternatives: Teach text_poke_bp() to emulate instructions) Peter Zijlstra
2019-10-09 13:26 ` Peter Zijlstra
2019-10-09 13:28 ` Peter Zijlstra
2019-10-09 14:26 ` Mathieu Desnoyers
2019-10-17 19:59 ` Peter Zijlstra
2019-10-03 13:05 ` [PATCH 1/3] x86/alternatives: Teach text_poke_bp() to emulate instructions Peter Zijlstra
2019-08-27 18:06 ` [PATCH 2/3] x86/alternatives,jump_label: Provide better text_poke() batching interface Peter Zijlstra
2019-10-02 16:34 ` Daniel Bristot de Oliveira
2019-10-03 5:50 ` Masami Hiramatsu
2019-08-27 18:06 ` [PATCH 3/3] x86/ftrace: Use text_poke() Peter Zijlstra
2019-10-02 16:35 ` Daniel Bristot de Oliveira
2019-10-02 18:21 ` Peter Zijlstra
2019-10-03 22:10 ` Steven Rostedt
2019-10-04 8:10 ` Daniel Bristot de Oliveira
2019-10-04 13:40 ` Steven Rostedt [this message]
2019-10-04 14:44 ` Daniel Bristot de Oliveira
2019-10-04 15:13 ` Steven Rostedt
2019-10-07 8:08 ` Peter Zijlstra
2019-10-11 7:01 ` Peter Zijlstra
2019-10-11 7:37 ` Daniel Bristot de Oliveira
2019-10-11 10:57 ` Peter Zijlstra
2019-10-11 13:11 ` Steven Rostedt
2019-10-04 11:22 ` Peter Zijlstra
2019-10-04 13:42 ` Steven Rostedt
2019-10-22 0:36 ` Alexei Starovoitov
2019-10-22 0:43 ` Steven Rostedt
2019-10-22 3:10 ` Alexei Starovoitov
2019-10-22 3:16 ` Steven Rostedt
2019-10-22 3:19 ` Steven Rostedt
2019-10-22 4:05 ` Alexei Starovoitov
2019-10-22 11:19 ` Steven Rostedt
2019-10-22 13:44 ` Steven Rostedt
2019-10-22 17:50 ` Alexei Starovoitov
2019-10-22 18:10 ` Steven Rostedt
2019-10-22 20:46 ` Alexei Starovoitov
2019-10-22 21:04 ` Steven Rostedt
2019-10-22 21:58 ` Alexei Starovoitov
2019-10-22 22:17 ` Steven Rostedt
2019-10-23 2:02 ` Steven Rostedt
2019-10-22 22:45 ` Andy Lutomirski
2019-10-22 23:21 ` Steven Rostedt
2019-10-22 23:49 ` Alexei Starovoitov
2019-10-23 4:20 ` Andy Lutomirski
2019-10-23 9:02 ` Peter Zijlstra
2019-10-23 16:23 ` Steven Rostedt
2019-10-23 17:42 ` Steven Rostedt
2019-10-23 19:34 ` Alexei Starovoitov
2019-10-23 20:08 ` Steven Rostedt
2019-10-23 22:36 ` Alexei Starovoitov
2019-10-22 3:55 ` Alexei Starovoitov
2019-10-03 5:52 ` Masami Hiramatsu
2019-08-28 7:22 ` [PATCH 0/3] Rewrite x86/ftrace to use text_poke() Song Liu
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