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Clock Synchronization in Cell BE Traces
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Clock Synchronization in Cell BE Traces
Marina Biberstein1 , Yuval Harel1 and Andre Heilper1 
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IBM Haifa Research Lab, Haifa University Campus, Haifa, 31905, Israel |
Abstract
Cell BE is a heterogeneous multicore processor that has been developed as a means for efficient execution of parallel and
vectorizable applications with high computation and memory requirements. The transition to multicores introduces the challenge
of providing tools that help programmers tune their code running on these architectures. Tracing tools, in particular, often
help locate performance problems related to thread and process communication.
A major impediment to implementing tracing on Cell is the absence of a common clock that can be accessed at low cost from
all cores. The OS clock is costly to access from the auxiliary cores and the hardware timers cannot be simultaneously set
on all the cores. In this paper, we describe an offline trace analysis that assigns wall-clock time to trace records based
on their thread-local time stamps and event order. Our experiments on several Cell SDK workloads show that the indeterminism
in assigning the wall-clock time is low, on average 20–40 clock ticks (1.4–2.8 μs for 14.8 MHz clock). We also show how various practical problems, such as the imprecision of time measurement, can be overcome.
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