linux-kernel - Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU mask

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:   Thu, 6 Apr 2017 12:58:27 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Mike Galbraith <efault@....de>, Ingo Molnar <mingo@...e.hu>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>
Subject: Re: [RFC PATCH] kernel: sched: Provide a pointer to the valid CPU
 mask

On Thu, 6 Apr 2017, Peter Zijlstra wrote:
> On Thu, Apr 06, 2017 at 11:25:42AM +0200, Sebastian Andrzej Siewior wrote:
> > > I.e. just have a counter and these two APIs:
> > > 
> > >         static inline void migrate_disable(void)
> > >         {
> > >                 current->migration_disabled++;
> > plus
> > 	if (current->migration_disabled == 1)
> > 		get_online_cpus()
> 
> You want that other hotplug fast hack crap you have in rt, no?

As I said in the other mail, we certainly want to make get_online_cpus()
fast independently of RT. That's on our todo list anyway.

> Because mainline will not get anything other than prempt_disable() for
> migrate_disable().

I'm not yet convinced of that. There is enough stuff which pointlessly
disables preemption and works around the restrictions caused by that or
plays games with cpus_allowed just to stay on a particular cpu.

I know you don't like it because it imposes restrictions on schedulability,
but disabling preemption for a long time or playing cpus_allowed games has
the same and worse effects.

Thanks,

	tglx