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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
> >   


  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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