linux-kernel - Re: [PATCH v3 tip/core/timers 0/5] Crude timer-wheel latency hacks

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, 16 Jan 2014 14:44:40 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	darren@...art.com, fweisbec@...il.com, oleg@...hat.com, sbw@....edu
Subject: Re: [PATCH v3 tip/core/timers 0/5] Crude timer-wheel latency hacks

On Wed, Jan 15, 2014 at 08:02:03PM -0800, Paul E. McKenney wrote:
> Hello!
> 
> The following five patches provide some crude timer-wheel latency patches.
> I understand that a more comprehensive solution is in progress, but in the
> meantime, these patches work well in cases where a given CPU has either
> zero or one timers pending, which is a common case for NO_HZ_FULL kernels.
> Note that these patches do not help in the case where a given timer wheel
> has a pair of widely separated timers, while the more comprehensive
> solution is likely to handle more gracefully.  So, on the off-chance
> that this is helpful to someone, the individual patches are as follows:
> 
> 1.	Add ->all_timers field to tbase_vec to count all timers, not
> 	just the non-deferrable ones.
> 
> 2.	Avoid jiffy-at-a-time stepping when the timer wheel is empty.
> 
> 3.	Avoid jiffy-at-a-time stepping when the timer wheel transitions
> 	to empty.
> 
> 4.	Avoid jiffy-at-a-time stepping after a timer is added to an
> 	initially empty timer wheel.
> 
> 5.	Make internal_add_timer() update ->next_timer if ->active_timers == 0,
> 	courtesy of Oleg Nesterov.

They seem like perfectly fine bandaids ;-)

Acked-by: Peter Zijlstra <peterz@...radead.org>
--
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/