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From: Steven Rostedt <rostedt@goodmis.org>
To: Oscar Carter <oscar.carter@gmx.com>
Cc: Ingo Molnar <mingo@redhat.com>, Kees Cook <keescook@chromium.org>,
	linux-kernel@vger.kernel.org,
	kernel-hardening@lists.openwall.com, Jann Horn <jannh@google.com>
Subject: Re: [PATCH v2 2/2] kernel/trace: Remove function callback casts
Date: Fri, 24 Jul 2020 13:48:11 -0400	[thread overview]
Message-ID: <20200724134811.01704cbf@oasis.local.home> (raw)
In-Reply-To: <20200724134020.3160dc7c@oasis.local.home>

On Fri, 24 Jul 2020 13:40:20 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 24 Jul 2020 13:36:56 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > Which BTW, is supported by the following architectures:


> >   x86  

Ah, you can lose support on x86 if you don't enable DYNAMIC_FTRACE,
which is stupid to do. I only enabled disabling of DYNAMIC_FTRACE on
x86 to test it, as not all architectures have it, and I currently only
test on x86.

Without DYNAMIC_FTRACE enabled, you *always* call into the ftrace
infrastructure for *every* function. This adds something like 15 to 20%
overhead to the kernel. Did I say it was stupid to do so?

If you are going through all this work because some randconfig causes
this warning because it enables CONFIG_FUNCTION_TRACER but without
DYNAMIC_FTRACE enabled, then I strongly suggest you start spending your
time elsewhere, because it will be a big NAK on my part to add all this
intrusive code for a config used only for debugging the non
DYNAMIC_FTRACE case.

-- Steve

  reply	other threads:[~2020-07-24 17:48 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-19 15:50 [PATCH v2 0/2] kernel/trace: Remove function callback casts Oscar Carter
2020-07-19 15:50 ` [PATCH v2 1/2] kernel/trace: Prepare to remove " Oscar Carter
2020-07-19 15:50 ` [PATCH v2 2/2] kernel/trace: Remove " Oscar Carter
2020-07-21 18:05   ` Steven Rostedt
2020-07-24 16:19     ` Oscar Carter
2020-07-24 16:35       ` Steven Rostedt
2020-07-24 17:14         ` Oscar Carter
2020-07-24 17:24           ` Oscar Carter
2020-07-24 17:36           ` Steven Rostedt
2020-07-24 17:40             ` Steven Rostedt
2020-07-24 17:48               ` Steven Rostedt [this message]
2020-07-24 17:55               ` Oscar Carter
2020-07-24 18:34                 ` Steven Rostedt
2020-07-25 15:09                   ` Oscar Carter
2020-07-25 15:19                     ` Oscar Carter
2020-07-26 15:52                     ` Oscar Carter
2020-07-27 13:53                       ` Steven Rostedt
2020-07-31 14:41                         ` Oscar Carter

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