linux-kernel - Re: [RFC] Unify KVM kernel-space and user-space code into a single project

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:	Sun, 21 Mar 2010 14:27:10 +0100
From:	Gabor Gombas <gombasg@...ikabel.hu>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Anthony Liguori <anthony@...emonkey.ws>,
	Avi Kivity <avi@...hat.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	oerg Roedel <joro@...tes.org>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, ziteng.huang@...el.com,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Fr?d?ric Weisbecker <fweisbec@...il.com>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
 project

On Thu, Mar 18, 2010 at 05:13:10PM +0100, Ingo Molnar wrote:

> > Why does Linux AIO still suck?  Why do we not have a proper interface in 
> > userspace for doing asynchronous file system operations?
> 
> Good that you mention it, i think it's an excellent example.
> 
> The suckage of kernel async IO is for similar reasons: there's an ugly package 
> separation problem between the kernel and between glibc - and between the apps 
> that would make use of it.

No, kernel async IO sucks because it still does not play well with
buffered I/O. Last time I checked (about a year ago or so), AIO syscall
latencies were much worse when buffered I/O was used compared to direct
I/O. Unfortunately, to achieve good performance with direct I/O, you
need a HW RAID card with lots of on-board cache.

Gabor
--
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/