linux-kernel - Re: [PATCH][resubmit] x86: enable preemption in delay

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 for Android: free password hash cracker in your pocket

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

Date:	Wed, 18 Jun 2008 06:13:45 -0600
From:	"Gregory Haskins" <ghaskins@...ell.com>
To:	"Ingo Molnar" <mingo@...e.hu>, "Marin Mitov" <mitov@...p.bas.bg>,
	"Gregory Haskins" <GHaskins@...ell.com>
Cc:	"Andi Kleen" <andi-suse@...stfloor.org>,
	"Clark Williams" <clark.williams@...il.com>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Peter Zijlstra" <peterz@...radead.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>, <akpm@...l.org>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	"LKML" <linux-kernel@...r.kernel.org>,
	"linux-rt-users" <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH][resubmit] x86: enable preemption in delay

>>> On Wed, Jun 18, 2008 at  8:08 AM, in message <4858C286.BA47.005A.0@...ell.com>,
"Gregory Haskins" <ghaskins@...ell.com> wrote: 
>>>> On Wed, Jun 18, 2008 at  3:55 AM, in message <20080618075518.GD4135@...e.hu>,
> Ingo Molnar <mingo@...e.hu> wrote: 
> 
>> * Marin Mitov <mitov@...p.bas.bg> wrote:
>> 
>>> Why not something like that (do keep in mind I am not an expert :-):
>>> 
>>> static void delay_tsc(unsigned long loops)
>>> {
>>> 	get and store the mask of allowed cpus;
>>> 	/*     prevent the migration   */
>>> 	set the mask of allowed cpus to the current cpu only;
>>> 	/*     is it possible? could it be guaranteed?    */
>>> 	loop for the delay;
>>> 	restore the old mask of allowed cpus;
>>> }
>>> 
>>> You have got the idea. Could it be realized? Is it more expensive than 
>>> the current realization? So, comments, please.
>> 
>> hm, changing/saving/restorig cpus_allowed is really considered a 'heavy' 
>> operation compared to preempt_disable(). On a 4096 CPUs box cpus_allowed 
>> is 4096 bits which is half a kilobyte ...
>> 
>> preempt_disable()/enable() on the other hand only touches a single 
>> variable, (thread_info->preempt_count which is an u32)
>> 
>> 	Ingo
> 
> FWIW:  I had submitted some "migration disable" patches a while back that 
> would solve this without the cpus_allowed manipulations described here.  Its 
> more expensive than a preempt-disable (but its preemptible), yet its way 
> cheaper (and more correct / less racy) than chaning cpus_allowed.  I could 
> resubmit if there was any interest, though I think Ingo said he didnt like 
> the concept on the first pass.  Anyway, FYI.

Sorry, should have provided a reference:

http://lkml.org/lkml/2008/2/12/344

> 
> -Greg
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/