linux-kernel - Re: [linus:master] [fortify] 239d87327d: vm-scalability.throughput 17.3% improvement

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Message-ID: <202501091236.E3EDA2188@keescook>
Date: Thu, 9 Jan 2025 12:38:04 -0800
From: Kees Cook <kees@...nel.org>
To: kernel test robot <oliver.sang@...el.com>
Cc: oe-lkp@...ts.linux.dev, lkp@...el.com, linux-kernel@...r.kernel.org,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Nilay Shroff <nilay@...ux.ibm.com>,
	Yury Norov <yury.norov@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-hardening@...r.kernel.org
Subject: Re: [linus:master] [fortify]  239d87327d:  vm-scalability.throughput
 17.3% improvement

On Thu, Jan 09, 2025 at 08:51:44AM -0800, Kees Cook wrote:
> On Thu, Jan 09, 2025 at 02:57:58PM +0800, kernel test robot wrote:
> > kernel test robot noticed a 17.3% improvement of vm-scalability.throughput on:
> > 
> > commit: 239d87327dcd361b0098038995f8908f3296864f ("fortify: Hide run-time copy size from value range tracking")
> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> Well that is unexpected. There should be no binary output difference
> with that patch. I will investigate...

It looks like hiding the size value from GCC has the side-effect of
breaking memcpy inlining in many places. I would expect this to make
things _slower_, though. O_o

-- 
Kees Cook