linux-kernel - Re: [PATCH documentation 1/2] nohz1: Add documentation.

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: <516C371E.70402@linux.intel.com>
Date:	Mon, 15 Apr 2013 10:21:34 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	paulmck@...ux.vnet.ibm.com, Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu, Kevin Hilman <khilman@...aro.org>
Subject: Re: [PATCH documentation 1/2] nohz1: Add documentation.

On 4/15/2013 9:53 AM, Christoph Lameter wrote:
> On Mon, 15 Apr 2013, Arjan van de Ven wrote:
>
>> to put the "cost" into perspective; programming a timer in one-shot mode
>> is some math on the cpu (to go from kernel time to hardware time),
>> which is a multiply and a shift (or a divide), and then actually
>> programming the hardware, which is at the cost of (approximately) a cachemiss
>> or two
>> (so give or take in the "hundreds" of cycles)
>> at least on moderately modern hardware (e.g. last few years)
>
> Well these are PCI transactions

eh no not on anything modern

they're touching the local apic which is core-local

> Ok then maybe go dynticks if we can save at least one timer tick?

switching between periodic versus not is actually non-trivial and much more expensive
(and complex) so not something you want to do all the time.
once during early boot is hard enough already

--
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/