netdev - Re: Kernel 4.6.7-rt13: Intel Ethernet driver igb causes huge latencies in cyclictest

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]

Date:   Mon, 17 Oct 2016 13:36:45 -0500
From:   Julia Cartwright <julia@...com>
To:     Richard Cochran <richardcochran@...il.com>
CC:     "Koehrer Mathias (ETAS/ESW5)" <mathias.koehrer@...s.com>,
        "Williams, Mitch A" <mitch.a.williams@...el.com>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        Sebastian Andrzej Siewior <sebastian.siewior@...utronix.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        Greg <gvrose8192@...il.com>
Subject: Re: Kernel 4.6.7-rt13: Intel Ethernet driver igb causes huge
 latencies in cyclictest

On Sat, Oct 15, 2016 at 12:06:33AM +0200, Richard Cochran wrote:
> On Fri, Oct 14, 2016 at 08:58:22AM +0000, Koehrer Mathias (ETAS/ESW5) wrote:
> > @@ -753,7 +756,9 @@ u32 igb_rd32(struct e1000_hw *hw, u32 re
> >  	if (E1000_REMOVED(hw_addr))
> >  		return ~value;
> >  
> > +        trace_igb(801);
> >  	value = readl(&hw_addr[reg]);
> > +        trace_igb(802);
> 
> Nothing prevents this code from being preempted between the two trace
> points, and so you can't be sure whether the time delta in the trace
> is caused by the PCIe read stalling or not.

While that is certainly the case, and would explain the most egregious
of measured latency spikes, it doesn't invalidate the test if you
consider the valuable data point(s) to be the minimum and/or median
latencies.

   Julia