linux-kernel - Re: [RFC PATCH 00/11] sched: CFS low-latency features

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:	Fri, 27 Aug 2010 17:20:52 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tony Lindgren <tony@...mide.com>,
	Mike Galbraith <efault@....de>
Subject: Re: [RFC PATCH 00/11] sched: CFS low-latency features

On Fri, 27 Aug 2010, Mathieu Desnoyers wrote:
> * Paul E. McKenney (paulmck@...ux.vnet.ibm.com) wrote:
> > Why couldn't the timer_create() call record the start time, and then
> > compute the sleeps from that time?  So if timer_create() executed at
> > time t=100 and the period is 5, upon awakening and completing the first
> > invocation of the function in question, the thread does a sleep calculated
> > to wake at t=110.
> 
> Let's focus on the userspace thread execution, right between the samping of the
> current time and the call to sleep:
> 
>   Thread A
>   current_time = read current time();
>   sleep(period_end - current_time);
> 
> If the thread is preempted between these two operations, then we end up sleeping
> for longer than what is needed. This kind of imprecision will add up over time,
> so that after e.g. one day, instead of having the expected number of timer
> executions, we'll have less than that. This kind of accumulated drift is an
> unwanted side-effect of using delays in lieue of real periodic timers.

Nonsense, that's why we provide clock_nanosleep(ABSTIME)

Thanks,

	tglx
--
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/