From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Matthew Helsley <mhelsley@vmware.com>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
David Woodhouse <dwmw2@infradead.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
ard.biesheuvel@linaro.org, Andy Lutomirski <luto@kernel.org>
Subject: Re: [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump_function"
Date: Sat, 6 Oct 2018 09:39:05 -0400 [thread overview]
Message-ID: <20181006093905.46276505@vmware.local.home> (raw)
In-Reply-To: <20181006121211.GA5663@hirez.programming.kicks-ass.net>
On Sat, 6 Oct 2018 14:12:11 +0200
Peter Zijlstra <peterz@infradead.org> wrote:
> On Fri, Oct 05, 2018 at 09:51:11PM -0400, Steven Rostedt wrote:
> > +#define arch_dynfunc_trampoline(name, def) \
> > + asm volatile ( \
> > + ".globl dynfunc_" #name "; \n\t" \
> > + "dynfunc_" #name ": \n\t" \
> > + "jmp " #def " \n\t" \
> > + ".balign 8 \n \t" \
> > + : : : "memory" )
>
> Bah, what is it with you people and trampolines. Why can't we, just like
> jump_label, patch the call directly?
>
> The whole call+jmp thing is silly, don't do that. It just wrecks I$ and
> is slower for no real reason afaict.
My first attempt was to do just that. But to add a label at the
call site required handling all the parameters too. See my branch:
ftrace/jump_function-v1 for how ugly it got (and it didn't work).
>
> Steve, also see:
>
> https://lkml.kernel.org/r/20181005081333.15018-1-ard.biesheuvel@linaro.org
Interesting. I don't have time to look at it at the moment to see what
was done, but will do so in the near future.
Remember, this was a proof of concept and even with the trampolines, it
showed a great level of improvement. One thought was to do a
"recordmcount.c" type of action to find where the calls were and patch
them directly at boot up. I tried to keep the API the same where this
could actually be done as an improvement later.
Perhaps a gcc plugin might work too.
I'll have to see what Ard did to handle the function parameters.
-- Steve
next prev parent reply other threads:[~2018-10-06 13:39 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-06 1:51 [POC][RFC][PATCH 0/2] PROOF OF CONCEPT: Dynamic Functions (jump functions) Steven Rostedt
2018-10-06 1:51 ` [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump_function" Steven Rostedt
2018-10-06 2:00 ` Steven Rostedt
2018-10-06 2:02 ` Steven Rostedt
2018-10-06 2:03 ` Steven Rostedt
2018-10-06 15:15 ` Steven Rostedt
2018-10-06 12:12 ` Peter Zijlstra
2018-10-06 13:39 ` Steven Rostedt [this message]
2018-10-06 15:13 ` Andy Lutomirski
2018-10-06 15:16 ` Steven Rostedt
2018-10-08 7:21 ` Peter Zijlstra
2018-10-08 8:33 ` Andy Lutomirski
2018-10-08 15:57 ` Peter Zijlstra
2018-10-08 16:29 ` Andy Lutomirski
2018-10-08 16:39 ` Steven Rostedt
2018-10-08 16:39 ` Peter Zijlstra
2018-10-08 17:25 ` Andy Lutomirski
2018-10-08 17:30 ` Ard Biesheuvel
2018-10-08 17:42 ` Andy Lutomirski
2018-10-08 17:44 ` Jiri Kosina
2018-10-08 17:45 ` Ard Biesheuvel
2018-10-08 17:47 ` Andy Lutomirski
2018-10-09 2:17 ` Josh Poimboeuf
2018-10-09 3:57 ` Steven Rostedt
2018-10-10 17:52 ` Josh Poimboeuf
2018-10-10 18:03 ` Andy Lutomirski
2018-10-10 18:16 ` Josh Poimboeuf
2018-10-10 18:17 ` Josh Poimboeuf
2018-10-10 21:13 ` Andy Lutomirski
2018-10-11 3:07 ` Josh Poimboeuf
2018-10-11 12:52 ` Josh Poimboeuf
2018-10-11 16:20 ` Andy Lutomirski
2018-10-10 18:33 ` Josh Poimboeuf
2018-10-10 18:56 ` Steven Rostedt
2018-10-10 20:16 ` Josh Poimboeuf
2018-10-10 20:57 ` Andy Lutomirski
2018-10-08 16:31 ` Steven Rostedt
2018-10-08 11:30 ` Ard Biesheuvel
2018-10-09 3:44 ` Masami Hiramatsu
2018-10-09 3:55 ` Steven Rostedt
2018-10-09 16:04 ` Masami Hiramatsu
2018-10-09 8:59 ` David Laight
2018-10-06 1:51 ` [POC][RFC][PATCH 2/2] tracepoints: Implement it with dynamic functions Steven Rostedt
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