linux-kernel - Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature

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: <alpine.DEB.2.20.1610261322580.4983@nanos>
Date:   Wed, 26 Oct 2016 13:24:27 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Tim Chen <tim.c.chen@...ux.intel.com>, rjw@...ysocki.net,
        mingo@...hat.com, bp@...e.de, x86@...nel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, jolsa@...hat.com,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling
 feature

On Wed, 26 Oct 2016, Peter Zijlstra wrote:
> On Wed, Oct 26, 2016 at 12:49:36PM +0200, Thomas Gleixner wrote:
> 
> > > +	/*
> > > +	 * ITMT capability automatically enables ITMT
> > > +	 * scheduling for small systems (single node).
> > > +	 */
> > > +	if (topology_num_packages() == 1)
> > > +		sysctl_sched_itmt_enabled = 1;
> > 
> > I really hate this. This is policy and the kernel should not impose
> > policy. Why would I like to have this enforced on my single socket XEON
> > server?
> 
> So this really wants to be enabled by default; otherwise nobody will use
> this, and it really does help single threaded workloads.

Fair enough. Then this wants to be documented.
 
> There were reservations on the multi-socket case of ITMT, maybe it would
> help to spell those out in great detail here. That is, have the comment
> explain the policy instead of simply stating what the code does (which
> is always bad comment policy, you can read the code just fine).

What is the objection for multi sockets? If it improves the behaviour then
why would this be a bad thing for multi sockets?

Thanks,

	tglx