linux-kernel - Re: [PATCH 1/2] x86/nmi: Optimize the check for being in the repeat

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Message-ID: <20170310072056.GA3762@gmail.com>
Date:   Fri, 10 Mar 2017 08:20:56 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] x86/nmi: Optimize the check for being in the
 repeat_nmi code


* Andy Lutomirski <luto@...capital.net> wrote:

> > It had nothing to do with speedup. Linus said that the current code makes the 
> > assembly programmer in him die a little. I want to cure that.
> 
> One might argue that the world would be a better place if the assembly 
> programmer in some people died a little.

Joking aside, I'll bite: while in the kernel we try to avoid ever actually 
_writing_ new assembly code, assembly programming is still an invaluable skill, 
because it indirectly improves all the other 99% of non-assembly .c code:

 - Looking at the C compiler's assembly output tells us how close the code is to
   optimal.

 - Being able to tell whether our C abstractions are too far removed from how the
   compiler will map it to machine instructions is invaluable.

 - Being able to shape data structures and code in a machine-friendly way.

Much would be lost if the assembly programmer went extinct and it's no 
accident that annotated assembly output is just two <Enter> keys away
after launching 'perf top' or 'perf report'. The more developers know
assembly the better, IMHO.

Thanks,

	Ingo