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Message-ID: <20161022231717.GE3334@pc.thejh.net>
Date: Sun, 23 Oct 2016 01:17:17 +0200
From: Jann Horn <jann@...jh.net>
To: David Windsor <dwindsor@...il.com>
Cc: kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org>,
"Reshetova, Elena" <elena.reshetova@...el.com>,
Hans Liljestrand <ishkamiel@...il.com>
Subject: Re: HARDENED_ATOMIC benchmarks
On Sat, Oct 22, 2016 at 06:13:29PM -0400, David Windsor wrote:
> Hi,
>
> The following are the results of benchmarking HARDENED_ATOMIC. The
> benchmarks performed were dbench and a timed Linux kernel compile using the
> Phoronix test suite [1] on a Linux VirtualBox guest.
>
> dbench was chosen specifically to gauge the performance penalty involved in
> heavy usage of struct file->f_count, as this is one of the hottest users of
> atomic_t/atomic_long_t.
As far as I can tell, dbench doesn't actually exercise f_count all that much
because it doesn't use threads, it just forks, meaning that the file
descriptor table isn't shared, which in turn means that fdget() and fdput()
don't do any refcounting. (And even if it did use threads, it probably
wouldn't be testing the contended case.)
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