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Unformatted text preview: e of 1. We can clarify this idea of correct and incorrect instruction orderings with the help of a formalism known as a progress graph, which we introduce in the next section. Practice Problem 11.3:
Which of the following instruction orderings for badcnt.c are sequentially consistent? A. B. C. D.
À½ À¾ Ä½ Ä¾ Í½ Í¾ Ë¾ Ë½ Ì¾ Ì½ À½ À¾ Ä¾ Í¾ Ë¾ Í½ Ì¾ Ä½ Ë½ Ì½ À¾ Ä¾ À½ Ä½ Í½ Ë½ Í¾ Ë¾ Ì¾ Ì½ À¾ À½ Ä¾ Ä½ Ë¾ Í½ Í¾ Ë½ Ì¾ Ì½ . . . . Practice Problem 11.4:
Complete the table for the following sequentially consistent ordering of badcnt.c. Step 1 2 3 4 5 6 7 8 9 10 Thread 1 1 2 2 2 2 1 1 1 2 Instr
À½ Ä½ À¾ Ä¾ Í¾ Ë¾ Í½ Ë½ Ì½ Ì¾ %eax½ – %eax¾ – cnt 0 Does this ordering result in a correct value for cnt? 11.4.2 Progress Graphs
A progress graph models the execution of Ò concurrent threads as a trajectory through an Ò-dimensional Cartesian space. Each axis corresponds to the progress of thread . Each point ´Á½ Á¾ ÁÒ µ represents the state where thread , ( ½ Ò) has completed instruction Á ....
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- Spring '10
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