State-of-the art in FLOSS systems: two presentations by international guests


The CCSL is happy to invite everyone to attend to two high-level international speeches, offered by specialists on each field. Christoph Hellwig, linux kernel developer involved primarily with filesystems, will talk about the new disk cache mechanism in the kernel; and Ian Pratt, leader of the community, will talk about that community, the Xen project, plans for the future etc.

The presentations (in English) will be offered Monday, August 30th, from 14:00h to 16:00h (Christoph Hellwig) and from 16:00h to 18:00h (Ian Pratt), at the Antonio Gillioli room (IME/USP, building A).

Title: A future without barriers - disk cache control and I/O ordering in Linux
Date: Monday, 30/08/2010, at 14:00h
Where: Auditório Antonio Gillioli, bloco A, IME/USP
Speaker: Christoph Hellwig

Abstract: This presentation tells a tale of caches, ordering, lies and misconceptions. It all started when the disk started lying to us. When consumer disks started to implement volatile caches with write back semantics hell broke lose for existing filesystem implementation. Before that point they could rely on internal I/O ordering for providing data integrity, but now that disks signaled I/O completion before data actually was on stable storage this strategy fell flat.

Initially Linux like most other operating systems ignored this issue and let users chose between going really fast and actually having reliably storage, with default setting of cheap disks being lose, but fast. The concept of I/O barriers was introduced to solve that dilemma. The I/O barrier semantics implemented in Linux in 2002 mixed the cache control aspect with data ordering semantics inspired by the SCSI ordered tag commands, assuming that we can use these to offload ordering to hardware.  But in the eight years since no one managed to actually come up with an optimized implementation of this interface, leading to dramatic performance degradation over not using a cache at all for many workloads.

This year we finally designed scheme to replace barriers with a simpler cache control concept that overcomes this limitation, and this presentation explains how we overcame the limitations of the previous scheme.

About the speaker: Christoph Hellwig has been working with and on Linux for the last ten years, dealing with kernel-related issues much of the time. In addition he is or was involved with various other Open Source projects.

After a number of smaller network administration and programming contracts he worked for Caldera's German development subsidiary on various kernel and userlevel aspects of the OpenLinux distribution.

Since 2004 he has been running his own business focusing on consulting, training and contracting work in the OpenSource hemisphere. Specializing on Linux filesystems and storage he is also active in bordering areas such as virtualization and networking. He has worked for well known customers such as Dell, SGI, IBM, Red Hat and startups like LeftHand Networks and Smapper Applied Data.

Title: with Ian Pratt
Date: Monday, 30/08/2010, at 16:00h
Where: Auditório Antonio Gillioli, bloco A, IME/USP
Speaker: Ian Pratt

Abstract: houses the open-source hypervisor Xen. Founded and leaded by Ian Pratt, the community benefits from contributions by senior engineers from over 50 hardware, software, and security providers. This presentation will talk about the project, the community, and ongoing efforts.

About the speaker: Ian Pratt is the chief architect of the Xen project, and chairman of He has played a key role in both the architecture of Xen and formation of industry partnerships that led to the emergence of Xen as the leading open source virtualization technology. Ian was a member of faculty at the University of Cambridge Computer Laboratory, where he led the Systems Research Group for over 7 years. He was a founder of XenSource, and is now VP for Advanced Products at Citrix.

29/Aug (2010), 21:00 - 30/Aug (2010), 20:59