linux-kernel - RE: Scheduler benchmarks

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: <e8acd1a8444846b196d5fa1fe45806bb@AcuMS.aculab.com>
Date:   Wed, 19 Aug 2020 14:36:25 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Bernd Petrovitsch' <bernd@...rovitsch.priv.at>,
        Muni Sekhar <munisekharrms@...il.com>
CC:     peter enderborg <peter.enderborg@...y.com>,
        Greg KH <greg@...ah.com>,
        kernelnewbies <kernelnewbies@...nelnewbies.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>
Subject: RE: Scheduler benchmarks

From: Bernd Petrovitsch
> Sent: 19 August 2020 11:22
> 
> On 19/08/2020 10:16, Muni Sekhar wrote:
> > On Tue, Aug 18, 2020 at 11:45 PM peter enderborg
> > <peter.enderborg@...y.com> wrote:
> [...]
> >> On the 4.4 kernel you dont have
> >>
> >> +CONFIG_RETPOLINE=y
> >> +CONFIG_INTEL_RDT=y
> > Thanks! That is helpful. Yes, I see 4.4 kernel don't have the above
> > two config options.
> > What analysis can be done to narrow down the root cause?
> > Any example of reference could be helpful to understand.
> 
> I haven't checked the date of the older kernel but Spectre+
> Meltdown mitigation costs a lot (20%-30% speed IIRC, out
> of the top of my head).

It depends greatly on the benchmark.

Page table separation has a massive effect on anything that
does a lot of short system calls.
There may be some mitigation in very recent hardware.
And I can't remember if it gets disabled for 'root' processes
(which can read kernel memory anyway).

It is definitely worth building a kernel with the mitigations
disabled  - if only to check that they are responsible.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)