270 research outputs found
Near-Memory Address Translation
Memory and logic integration on the same chip is becoming increasingly cost
effective, creating the opportunity to offload data-intensive functionality to
processing units placed inside memory chips. The introduction of memory-side
processing units (MPUs) into conventional systems faces virtual memory as the
first big showstopper: without efficient hardware support for address
translation MPUs have highly limited applicability. Unfortunately, conventional
translation mechanisms fall short of providing fast translations as
contemporary memories exceed the reach of TLBs, making expensive page walks
common.
In this paper, we are the first to show that the historically important
flexibility to map any virtual page to any page frame is unnecessary in today's
servers. We find that while limiting the associativity of the
virtual-to-physical mapping incurs no penalty, it can break the
translate-then-fetch serialization if combined with careful data placement in
the MPU's memory, allowing for translation and data fetch to proceed
independently and in parallel. We propose the Distributed Inverted Page Table
(DIPTA), a near-memory structure in which the smallest memory partition keeps
the translation information for its data share, ensuring that the translation
completes together with the data fetch. DIPTA completely eliminates the
performance overhead of translation, achieving speedups of up to 3.81x and
2.13x over conventional translation using 4KB and 1GB pages respectively.Comment: 15 pages, 9 figure
Editorial: Molecular basis of the response of photosynthetic apparatus to light and temperature stress
2 Pags. This article was submitted to
Plant Cell Biology,
a section of the journal
Frontiers in Plant Science.- © 2017 Picorel, Alfonso and Velitchkova. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).Work in the laboratory of RP and MA was supported by
Grant AGL2014-55300-R from Ministry of Economy and
Competitiveness (MINECO) of Spain. Work in MV laboratory
was supported by Swiss National Science Foundation under
BSRP (IZEBZO-143169/1).Peer reviewe
Aislamiento y caracterización de mutantes Rhodospirillum rubrum con alteraciones en el centro fotosintético de reacción
Tesis Univ. Complutense de Madrid.Fac. de Ciencias BiológicasTRUEProQuestpu
Aislamiento y caracterización de mutantes Rhodospirillum rubrum con alteraciones en el centro fotosintético de reacción
Tesis Univ. Complutense de Madrid.Fac. de Ciencias BiológicasTRUEProQuestpu
Near-Memory Address Translation
Virtual memory (VM) is a crucial abstraction in modern computer systems at any scale, from handheld devices to datacenters. VM provides programmers the illusion of an always sufficiently large and linear memory, making programming easier. Although the core components of VM have remained largely unchanged since early VM designs, the design constraints and usage patterns of VM have radically shifted from when it was invented. Today, computer systems integrate hundreds of gigabytes to a few terabytes of memory, while tightly integrated heterogeneous computing platforms (e.g., CPUs, GPUs, FPGAs) are becoming increasingly ubiquitous. As there is a clear trend towards extending the CPU's VM to all computing elements in the system for an efficient and easy to use programming model, the continuous demand for faster memory accesses calls for fast translations to terabytes of memory for any computing element in the system. Unfortunately, conventional translation mechanisms fall short of providing fast translations as contemporary memories exceed the reach of today's translation caches, such as TLBs. In this thesis, we provide fundamental insights into the reason why address translation sits on the critical path of accessing memory. We observe that the traditional fully associative flexibility to map any virtual page to any page frame precludes accessing memory before translating. We study the associativity in VM across a variety of scenarios by classifying page faults using the 3C model developed for caches. Our study demonstrates that the full associativity of VM is unnecessary, and only modest associativity is required. We conclude that capacity and compulsory misses---which are unaffected by associativity---dominate, while conflict misses rapidly disappear as the associativity of VM increases. Building on the modest associativity requirements, we propose a distributed memory management unit close to where the data resides to reduce or eliminate the TLB miss penalty
Pigment Content of D1-D2-Cytochrome b559 Reaction Center Preparations after Removal of CP47 Contamination: An Immunological Study
5 pages, figures, and tables statistics.Isolated D1 -D2-cytochrome b559 photosystem I1 reaction center preparations with pigment
stoichiometry higher than 4 chlorophylls per 2 pheophytins can be contaminated with CP47 proximal
antenna complex. Reaction centers prepared by a modification of the Nanba-Satoh procedure and
containing about 6 chlorophylls per 2 pheophytins showed immuno-cross-reactivity when probed with a
monoclonal antibody raised against the CP47 polypeptide. Furthermore, they could be fractionated
successfully by Superose- 12 sieve chromatography into two different populations. The first few fractions
off the column contained a more definitive 435 nm shoulder corresponding to increased chlorophyll content,
and showed strong immuno-cross-reactivity with the CP47 antibody. The peak fractions off the column
displayed a less prominent 435 nm shoulder, and did not cross-react with the antibody. Moreover, when
a 6-chlorophyll preparation was mixed with Sepharose beads coupled to CP47 antibody, the eluted material
corresponded to a preparation of about 4 chlorophylls per 2 pheophytins and did not show any crossreaction
with the antibody against CP47. The amount of CP47 protein in the 6-chlorophyll preparation
as quantitated using Coomassie Blue staining or from gel blots was sufficient to account for most of the
extra 2 chlorophylls. We conclude that D 1 -D2-cytochrome b559 preparations containing more than 4
chlorophylls per 2 pheophytins can be contaminated with small amounts of CP47-D1 -D2-Cyt b559
complex and that native photosystem I1 reaction centers contain 4 core chlorophylls per 2 pheophytins.Peer reviewe
Design Guidelines for High-Performance SCM Hierarchies
With emerging storage-class memory (SCM) nearing commercialization, there is
evidence that it will deliver the much-anticipated high density and access
latencies within only a few factors of DRAM. Nevertheless, the
latency-sensitive nature of memory-resident services makes seamless integration
of SCM in servers questionable. In this paper, we ask the question of how best
to introduce SCM for such servers to improve overall performance/cost over
existing DRAM-only architectures. We first show that even with the most
optimistic latency projections for SCM, the higher memory access latency
results in prohibitive performance degradation. However, we find that
deployment of a modestly sized high-bandwidth 3D stacked DRAM cache makes the
performance of an SCM-mostly memory system competitive. The high degree of
spatial locality that memory-resident services exhibit not only simplifies the
DRAM cache's design as page-based, but also enables the amortization of
increased SCM access latencies and the mitigation of SCM's read/write latency
disparity.
We identify the set of memory hierarchy design parameters that plays a key
role in the performance and cost of a memory system combining an SCM technology
and a 3D stacked DRAM cache. We then introduce a methodology to drive
provisioning for each of these design parameters under a target
performance/cost goal. Finally, we use our methodology to derive concrete
results for specific SCM technologies. With PCM as a case study, we show that a
two bits/cell technology hits the performance/cost sweet spot, reducing the
memory subsystem cost by 40% while keeping performance within 3% of the best
performing DRAM-only system, whereas single-level and triple-level cell
organizations are impractical for use as memory replacements.Comment: Published at MEMSYS'1
Copper effect on cytochrome b559 of photosystem II under photoinhibitory conditions
The definitive version is available at www.blackwell-synergy.comToxic Cu(II) effect on Cytochrome b559 under aerobic photoinhibitory conditions was examined in two different PSII membrane preparations active in oxygen evolution. The preparations differ in the content of Cytochrome b559 redox potential forms. Difference absorption spectra showed that the presence of Cu(II) induced the oxidation of the high-potential form of Cytochrome b559 in the dark. Addition of hydroquinone reduced the total oxidised high-potential form of Cytochrome b559 present in Cu(II)-treated PSII membranes indicating that no conversion to the low-potential form took place. Spectroscopic determinations of Cytochrome b559 during photoinhibitory treatment showed slower kinetics of Cu(II) effect on Cytochrome b559 as compared to the rapid loss of oxygen evolution activity in the same conditions. This result indicates that Cytochrome b559 is affected after PSII centers are photoinhibited. The high-potential form was more sensitive to toxic Cu(II) action than the low-potential form under illumination at pH 6.0. The content of the high-potential form of Cytochrome b559 was completely lost, however the low-potential content was unaffected in these conditions. This loss did not involve cytochrome protein degradation. Results are discussed in terms of different binding properties of the heme iron to the protonated or unprotonated histidine ligand in the high-potential and low-potential forms of Cytochrome b559, respectively.M. Bernal was recipient of an I3P Programme fellowship from Consejo Superior de Investigaciones Científicas. This work was supported by the Dirección General de Investigación (Grant BMC2002-00031) to R.P. and Gobierno de Aragón (Grant P015/2001) to I.Y., and it has been done within GC DGA 2002 Program of Gobierno de Aragón.Peer reviewe
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