linux-kernel - Re: [RFC] sched: Add a new lockless wake-from-idle implementation

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: <CAFTL4hwRYMa+Ouc=VRCnG6g=18JxRJ1yYHKxiikBEdRP_f-k2Q@mail.gmail.com>
Date:	Thu, 13 Feb 2014 15:49:06 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <bitbucket@...ine.de>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] sched: Add a new lockless wake-from-idle implementation

2014-02-13 2:40 GMT+01:00 Andy Lutomirski <luto@...capital.net>:
> This is a strawman proposal to simplify the idle implementation, eliminate
> a race

Please describe the race in question.

>
> Benefits over current code:
>  - ttwu_queue_remote doesn't use an IPI unless needed
>  - The diffstat should speak for itself :)

Actually referring to the diffstat alone sounds dangerous here. Sure
this simplifies the code, I'm all for negative diffstat, and probably
it avoids a few IPIs, but this comes at the cost of added non-cheap
atomic_xchg() calls in some critical fastpath like resched_task()
path, the timer enqueue path and the inner idle loop.

So it's not like this all comes for free. I'm not saying we don't want
it but at least some serious measurements is needed.
--
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/