linux-kernel - Re: [GIT PULL] kdbus for 4.1-rc1

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 for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 27 Apr 2015 15:14:49 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Lukasz Skalski <l.skalski@...sung.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tom Gundersen <teg@...m.no>, Jiri Kosina <jkosina@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daniel Mack <daniel@...que.org>,
	David Herrmann <dh.herrmann@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>
Subject: Re: [GIT PULL] kdbus for 4.1-rc1

On Mon, Apr 27, 2015 at 3:00 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> IOW, all the people who say that it's about avoiding context switches
> are probably just full of shit. It's not about context switches, it's
> about bad user-level code.

Just to make sure, I did a system-wide profile (so that you can
actually see the overhead of context switching better), and that
didn't change the picture.

The scheduler overhead *might* be 1% or so.

So really. The people who talk about how kdbus improves performance
are just full of sh*t. Yes, it improves things, but the improvement
seems to be 100% "incidental", in that it avoids a few trips down the
user-space problems.

The real problems seem to be in dbus memory management (suggestion:
keep a small per-thread cache of those message allocations) and to a
smaller degree in the crazy utf8 validation (why the f*ck does it do
that anyway?), with some locking problems thrown in for good measure.

                              Linus
--
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/