The number of cores integrated onto a single die is expected to climb steadily in the foreseeable future. This move to many-core chips is driven by a need to optimize performance per watt. How best to connect these cores and how to program the resulting many-core processor, however, is an open research question. Designs vary from GPUs to cache-coherent shared memory multiprocessors to pure distributed memory chips. The 48-core SCC processor reported in this paper is an intermediate case, sharing traits of message passing and shared memory architectures. The hardware has been described elsewhere. In this paper, we describe the programmer's view of this chip. In particular we describe RCCE: the native message passing model created for the SCC processor.Index Terms-many-core processors, message passing APIs, non-cache-coherent shared memory.

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Convolvulus arvensis, commonly known as wild morning-glory or bindweed, is the most noxious weed pest in orchards and fields of California and other western states. No satisfactory method has been devised for its control or eradication. It occupies the most fertile soils and the area of infestation increases every year.We have been unsuccessful in our efforts to control it by the methods usually recommended for the control of perennial weeds, viz.: keeping the stems cut below the surface of the ground. This failure is due to the large storage capacity of the root and its ability to produce new shoots. Experiments in which the stems have been kept from appearing above the ground for three years have not given satisfactory results. GRAY' states that roots taken from a depth of 14 feet are capable of producing new plants. Roots have been found at even greater depths.The plants normally possess a tap root with many lateral branches. These roots are capable of producing shoot buds which develop into a complex network of rhizomes permeating the soil from a considerable depth. These rhizomes appear at the surface at irregular periods as leafy shoots. The cutting of the roots stimulates the production of many buds which in turn increase the number of rhizomes and leafy shoots. Cutting with a weed-cutter, when the soil moisture is abundant, tends to spread the severed parts over the field where they may grow and produce new centers of infestation. Roots cut or killed to a depth of four feet have produced rhizomes which have reached the surface within a few months.As early as 1915 GRAY2 found that certain arsenical sprays, when applied to the foliage, were capable of killing not only all parts of the plants above ground, but also the roots to a depth of several feet. In 19193 he gave a detailed report of his experiments concluding that the stage of maturity of the plant and the amount of moisture in the atmosphere were two controlling factors involved in his results.Since the methods devised by GRAY failed to give satisfaction in many parts of the state, it was deemed advisable to test thoroughly the behavior 1 GRAY, G. P. Tests of chemical means for the control of weeds. Univ. of Calif. pub. in Agr. Sci. 4: 77-79. 1919. 2 GRAY, G. P. Spraying for the control of wild morning-glory within the fog belt. Calif. Agr. Exp. Sta. Cir. 168: 1-7. 1917.. 3 Loc. cit., passim. 503 www.plantphysiol.org on July 15, 2020 -Published by Downloaded from

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