linux-kernel - Re: [PATCH 00/20] objtool: UACCESS validation v3

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Message-ID: <20190310131620.GL2482@worktop.programming.kicks-ass.net>
Date:   Sun, 10 Mar 2019 14:16:20 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Anvin <hpa@...or.com>,
        Julien Thierry <julien.thierry@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>, valentin.schneider@....com,
        Brian Gerst <brgerst@...il.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Slavomir Kaslev <kaslevs@...are.com>
Subject: Re: [PATCH 00/20] objtool: UACCESS validation v3

On Thu, Mar 07, 2019 at 01:18:41PM -0500, Steven Rostedt wrote:
> On Thu, 7 Mar 2019 09:45:35 -0800
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > On Thu, Mar 7, 2019 at 9:38 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > Also; it seems to me that something PT, or maybe even simply:
> > >
> > >   perf -e branches -e branch-misses
> > >
> > > would get you similar or sufficient information.  

> I currently have one of my engineers looking at the data and may be
> sending patches soon. It's basically an entry level way to get into
> kernel development. Note, no patch will be sent just because of the
> data from the profiling. The task is to look at and understand the
> code, and see if it can be optimized (with likely/unlikely or flow
> changes). It's a way to get a better understanding of the kernel in
> various locations. It is by no means "profiler said this, lets change
> it." All changes must be rational, and make sense. The profiler is only
> used to help find those places.

Can't you just have those same engineers look at perf data? This seems
like a very expensive and convoluted way of getting something.