linux-kernel - Re: [PATCH RESEND v4] sched/fair: Add advisory flag for borrowing a timeslice

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] [day] [month] [year] [list]

Date:	Tue, 13 Jan 2015 12:25:16 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Khalid Aziz <khalid.aziz@...cle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>, corbet@....net,
	mingo@...hat.com, hpa@...or.com, akpm@...ux-foundation.org,
	rientjes@...gle.com, ak@...ux.intel.com, mgorman@...e.de,
	raistlin@...ux.it, kirill.shutemov@...ux.intel.com,
	atomlin@...hat.com, avagin@...nvz.org, gorcunov@...nvz.org,
	serge.hallyn@...onical.com, athorlton@....com, oleg@...hat.com,
	vdavydov@...allels.com, daeseok.youn@...il.com,
	keescook@...omium.org, yangds.fnst@...fujitsu.com,
	sbauer@....utah.edu, vishnu.ps@...sung.com, axboe@...com,
	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-api@...r.kernel.org
Subject: Re: [PATCH RESEND v4] sched/fair: Add advisory flag for borrowing a
 timeslice

On Tue, Dec 23, 2014 at 01:46:58PM -0500, Rik van Riel wrote:
> An uncontended futex is taken without ever going into kernel
> space. Adaptive spinning allows short duration futexes to be
> taken without going into kernel space.

The going into kernel is a red herring afaict, a no-op syscall costs ~180
cycles or something like that. So sure you can do a wee spin (~90 cycles
to try and amortize that), but I really doubt that this is the problem.
--
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/