linux-kernel - Re: [RFC PATCH] makefile: add debug option to enable function aligned on 32 bytes

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Date:   Thu, 23 Jul 2020 17:57:04 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        andi.kleen@...el.com, ying.huang@...el.com,
        andriy.shevchenko@...el.com
Subject: Re: [RFC PATCH] makefile: add debug option to enable function
 aligned on 32 bytes

On Thu, 23 Jul 2020 14:29:33 +0800 Feng Tang <feng.tang@...el.com> wrote:

> > > gcc has an option '-falign-functions=n' to force text aligned, and with
> > > that option enabled, some of those performance changes will be gone,
> > > like [1][2][3].
> > > 
> > > Add this option so that developers and 0day can easily find performance
> > > bump caused by text alignment change,
> > 
> > Would they use it this way, or would they simply always enable the
> > option to reduce the variability?
> 
> I may mis-understood it in my last reply. If you are asking about how
> will developers and 0day use this option, for 0day, I've talked with
> 0day folks, they may just enable it by default, as 0day cares more about
> the performance delta caused by a commit (Adding Philip and Rong from
> 0day).

OK, thanks, I suspected as much.

The patch is so simple and probably-will-work, I guess we toss it in
there and see.

However it would be good if the 0day people could use it for a while
and then provide some feedback on whether it is actually proving
useful.  If not, we get to remove some stuff.