linux-kernel - Re: [PATCH v2 1/2] init/initramfs.c: allow asynchronous unpacking

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Date:   Thu, 11 Mar 2021 10:02:27 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jessica Yu <jeyu@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2 1/2] init/initramfs.c: allow asynchronous unpacking

On Wed, Mar 10, 2021 at 5:45 PM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
>
> Hm, gcc does elide the test of the return value, but jumps back to a
> place where it always loads state from its memory location and does the
> whole switch(). To get it to jump directly to the code implementing the
> various do_* helpers it seems one needs to avoid that global variable
> and instead return the next state explicitly. The below boots, but I
> still can't see any measurable improvement on ppc.

Ok. That's definitely the right way to do efficient statemachines that
the compiler can actually generate ok code for, but if you can't
measure the difference I guess it isn't even worth doing.

Thanks for checking, though.

        Linus