linux-kernel - Re: [PATCH 4/6] lib/refcount: Move bulk of REFCOUNT

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Message-ID: <20190809160428.smumdvimrtn7rv6u@willie-the-truck>
Date:   Fri, 9 Aug 2019 17:04:28 +0100
From:   Will Deacon <will@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Hanjun Guo <guohanjun@...wei.com>,
        Jan Glauber <jglauber@...vell.com>
Subject: Re: [PATCH 4/6] lib/refcount: Move bulk of REFCOUNT_FULL
 implementation into header

On Fri, Aug 02, 2019 at 07:23:07PM -0700, Kees Cook wrote:
> On Fri, Aug 02, 2019 at 08:52:22PM +0200, Peter Zijlstra wrote:
> > On Fri, Aug 02, 2019 at 11:09:58AM +0100, Will Deacon wrote:
> > > In an effort to improve performance of the REFCOUNT_FULL implementation,
> > > move the bulk of its functions into linux/refcount.h. This allows them
> > > to be inlined in the same way as if they had been provided via
> > > CONFIG_ARCH_HAS_REFCOUNT.
> > 
> > Hehe, they started out this way, then Linus said to stuff them in a C
> > file :-)
> 
> I asked this at the time and didn't quite get a straight answer; Linus's
> request was private:
> 
> https://lore.kernel.org/lkml/20170213180020.GK6500@twins.programming.kicks-ass.net/
> 
> It seemed sensible to me (then and now) to have them be inline if there
> were so many performance concerns about it, etc. Was it just the image
> size bloat due to the WARNs? So... since we're back to this topic. Why
> should they not be inline?

I mean, I can always just move this into an arm64-specific implementation
if I have to, but it seems a shame given that it's completely generic and
seems to perform just as well as the x86-specific implementation on my
laptop.

Will