linux-kernel - Re: [GIT PULL] adaptive spinning mutexes

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: <20090115180844.GL22472@elte.hu>
Date:	Thu, 15 Jan 2009 19:08:44 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Matthew Wilcox <matthew@....cx>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Gregory Haskins <ghaskins@...ell.com>,
	Andi Kleen <andi@...stfloor.org>,
	Chris Mason <chris.mason@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>,
	Peter Morreale <pmorreale@...ell.com>,
	Sven Dietrich <SDietrich@...ell.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [GIT PULL] adaptive spinning mutexes


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> > Has anyone found a non-synthetic benchmark where this makes a 
> > significant difference?  Aside from btrfs, I mean.
> 
> Yea, if you have some particular filesystem (or other subsystem) that 
> uses a global mutex, you'll obviously see way more contention. Btrfs may 
> not be _unique_ in this regard, but it's definitely doing something that 
> isn't good.
> 
> Btw, it's doing something that ext3 also used to do iirc, until we fixed 
> it to use spinlocks instead (the block group lock in particular).
> 
> Yeah - just double-checked. Commit c12b9866ea52 in the historical Linux 
> archive, from 2003. Which made block allocation protected by a per-group 
> spinlock, rather than lock_super().

btw., i think spin-mutexes have a design advantage here: in a lot of code 
areas it's quite difficult to use spinlocks - cannot allocate memory, 
cannot call any code that can sporadically block (but does not _normally_ 
block), etc.

With mutexes those atomicity constraints go away - and the performance 
profile should now be quite close to that of spinlocks as well.

	Ingo
--
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/