netdev - Re: [Intel-wired-lan] [PATCH] i40e: replace switch-statement with if-clause

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190121201213.4cb33c97@redhat.com>
Date:   Mon, 21 Jan 2019 20:12:13 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     Paul Menzel <pmenzel@...gen.mpg.de>,
        Björn Töpel <bjorn.topel@...el.com>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        Netdev <netdev@...r.kernel.org>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>, brouer@...hat.com
Subject: Re: [Intel-wired-lan] [PATCH] i40e: replace switch-statement with
 if-clause

On Mon, 21 Jan 2019 17:53:45 +0100
Björn Töpel <bjorn.topel@...il.com> wrote:

> > If that jump tables are a common problem, I wonder, why the compiler
> > cannot be adapted to generate better performing code or an option passed
> > to the compiler.
> >  
> 
> It might make sense to use -fno-jump-tables or a better value for the
> case-values-threshold param for the i40e code. However, doing that
> would require a much broader testing, since there are a number of
> different places where a switch-statement is used. And depending on
> the context, a jump table might still be a better option.

I recently found out that it is possible to disable GCC attributes per
function basis.  See how I played with it here:
  https://github.com/xdp-project/xdp-project/blob/master/areas/dma/dma01_test_hellwig_direct_dma.org#investigate-overhead-of-bpf-indirect-retpoline

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer