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Dynamic frequency and voltage scaling (DVFS) techniques have been widely used for meeting energy constraints. Single-chip many-core systems bring new challenges owing to the large number of operating points and the shift to message passing interface (MPI) from shared memory communication. DVFS, however, has been mostly studied on single-chip systems with one or few cores, without considering the impact of the communication among cores. This paper evaluates the impact of frequency scaling on the performance and power of many-core systems with MPI. We conduct experiments on the Single-Chip Cloud Computer (SCC), an experimental many-core processor developed by Intel. The paper first introduces the run-time monitoring infrastructure and the application suite we have designed for an in-depth evaluation of the SCC. We provide an extensive analysis quantifying the effects of frequency perturbations on performance and energy efficiency. Experimental results show that runtime communication patterns lead to significant differences in power/performance tradeoffs in many-core systems with MPI.

Children undergoing neurosurgical resection are at high risk for postoperative nausea and vomiting. Ondansetron, a selective serotonergic (5-HT3) antagonist, is effective in reducing postoperative vomiting in several high-risk populations. In a prospective, randomized study, we compared the prophylactic use of intravenous ondansetron, 0.15 mg/kg, versus placebo for the prevention of emesis in 60 children, aged 2-18 yr, undergoing craniotomies for resective procedures. Patients with preoperative emesis were excluded from the study. All patients were tracheally extubated at the conclusion of surgery, and each episode of emesis during the first 24 postoperative hours was recorded. For the entire 24-h interval, the incidence of emesis in children who received ondansetron (57%) was not significantly different from that in those who received placebo (66%); however, in the first 8 h, the incidence was 25% (ondansetron) vs 44% (placebo) (P = not significant). In those receiving placebo, there was no difference in emesis between patients undergoing operations above versus below the tentorium. Although our sample size was too small to completely exclude any beneficial effect, ondansetron appears ineffective in preventing postoperative emesis in this patient population.

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