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See detailPAG: Private and Accountable Gossip
Decouchant, Jérémie UL; Ben Mokhtar, Sonia; Petit, Albin et al

Scientific Conference (2016, June 28)

A large variety of content sharing applications rely, at least partially, on gossip-based dissemination protocols. However, these protocols are subject to various types of faults, among which selfish ... [more ▼]

A large variety of content sharing applications rely, at least partially, on gossip-based dissemination protocols. However, these protocols are subject to various types of faults, among which selfish behaviours performed by nodes that benefit from the system without contributing their fair share to it. Accountability mechanisms (e.g., PeerReview, AVMs, FullReview), which require that nodes log their interactions with others and periodically inspect each others’ logs are effective solutions to deter faults. However, these solutions require that nodes disclose the content of their logs, which may leak sensitive information about them. Building on a monitoring infrastructure and on homomorphic cryptographic procedures, we propose in this paper PAG, the first accountable and partially privacy-preserving gossip protocol. We assess PAG theoretically using the ProVerif cryptographic protocol verifier and evaluate it experimentally using both a real deployment on a cluster of 48 machines and simulations. The performance evaluation of PAG, performed using a video live streaming application, shows that it is compatible with the visualisation of live video content on commodity Internet connections. Furthermore, PAG’s bandwidth consumption inherits the desirable scalability properties of gossip when the number of users in the system grows. [less ▲]

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See detailAcTinG: Accurate Freerider Tracking in Gossip
Decouchant, Jérémie UL; Ben Mokhtar, Sonia; Quéma, Vivien

Scientific Conference (2014, October 09)

Gossip-based content dissemination protocols are a scalable and cheap alternative to centralised content sharing systems. However, it is well known that these protocols suffer from rational nodes, i.e ... [more ▼]

Gossip-based content dissemination protocols are a scalable and cheap alternative to centralised content sharing systems. However, it is well known that these protocols suffer from rational nodes, i.e., nodes that aim at downloading the content without contributing their fair share to the system. While the problem of rational nodes that act individually has been well addressed in the literature, colluding rational nodes is still an open issue. Indeed, LiFTinG, the only existing gossip protocol addressing this issue, yields a high ratio of false positive accusations of correct nodes. In this paper, we propose AcTinG, a protocol that prevents rational collusions in gossip-based content dissemination protocols, while guaranteeing zero false positive accusations. We assess the performance of AcTinG on a testbed comprising 400 nodes running on 100 physical machines, and compare its behaviour in the presence of colluders against two state-of-the-art protocols: BAR Gossip that is the most robust protocol handling non-colluding rational nodes, and LiFTinG, the only existing gossip protocol that handles colluding nodes. The performance evaluation shows that AcTinG is able to deliver all messages despite the presence of colluders, whereas both LiFTinG and BAR Gossip suffer heavy message loss. It also shows that AcTinG is resilient to massive churn. Finally, using simulations involving up to a million nodes, we show that AcTinG exhibits similar scalability properties as standard gossip-based dissemination protocols. [less ▲]

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See detailLarge Pages May Be Harmful on NUMA Systems
Gaud, Fabien; Lepers, Baptiste; Decouchant, Jérémie UL et al

Scientific Conference (2014, June)

Application virtual address space is divided into pages, each requiring a virtual-to-physical translation in the page table and the TLB. Large working sets, common among modern applications, necessitate a ... [more ▼]

Application virtual address space is divided into pages, each requiring a virtual-to-physical translation in the page table and the TLB. Large working sets, common among modern applications, necessitate a lot of translations, which increases memory consumption and leads to high TLB and page fault rates. To address this problem, recent hardware introduced support for large pages Large pages require fewer translations to cover the same address space, so the associated problems diminish. We discover, however, that on systems with non-uniform memory access times (NUMA) large pages may fail to deliver benefits or even cause performance degradation. On NUMA systems the memory is spread across several physical nodes; using large pages may contribute to the imbalance in the distribution of memory controller requests and reduced locality of accesses, both of which can drive up memory latencies. Our analysis concluded that: (a) on NUMA systems with large pages it is more crucial than ever to use memory placement algorithms that balance the load across memory controllers and maintain locality; (b) there are cases when NUMA-aware memory placement is not sufficient for optimal performance, and the only resort is to split the offending large pages. To address these challenges, we extend an existing NUMA page placement algorithm with support for large pages. We demonstrate that it recovers the performance lost due to the use of large pages and makes their benefits accessible to applications [less ▲]

Detailed reference viewed: 63 (6 UL)