1756-ENBT,A-B,1756-ENBT
嵌入式多核處理器結(jié)構(gòu)
嵌人式多核處理器的結(jié)構(gòu)包括同構(gòu)(Symmetric)和異構(gòu)(Asymmetric)兩種。同構(gòu)是指內(nèi)部核的結(jié)構(gòu)是相同的,這種結(jié)構(gòu)目前廣泛應(yīng)用在PC多核處理器;而異構(gòu)是指內(nèi)部核的結(jié)構(gòu)是不同的,這種結(jié)構(gòu)常常在嵌入式領(lǐng)域使用,常見的是通用嵌入式處理器+DSP核。本文探究的嵌入式多核處理器采用同構(gòu)結(jié)構(gòu),實現(xiàn)同一段代碼在不同處理器上的并行執(zhí)行。
圖1 ARM SMP處理器結(jié)構(gòu)
在目前嵌入式領(lǐng)域中,使用的為ARM 處理器,因此以ARM 雙核處理器OMAP4430作為研究對象。ARM 對稱多處理(Symmetric Multi-Processing,SMP)結(jié)構(gòu)如圖1所示,根據(jù)程序的局部性原理,每一個處理器都具有私有的內(nèi)存(Local Memory),常見的是一級緩存(L1Cache)。然而,多個處理器之間又涉及到相互通信問題,因此在常見的ARM 處理器中使用二級緩存(L2 Cache)來解決這一問題?;趯ΨQ多處理器結(jié)構(gòu),所有的處理器(通常為2的倍數(shù))在硬件結(jié)構(gòu)上都是相同的,在使用系統(tǒng)資源上也是平等的。更重要的是,由于所有的處理器都有權(quán)利去訪問相同的內(nèi)存空間,在共享內(nèi)存區(qū)域中,任何一個進程或者線程都可以運行在任意一個處理器之上,這樣就使得程序的并行化成為可能。2在嵌入式多核平臺上進行并行化優(yōu)化,需要考慮以下問題:
?、?并行化程序的性能取決于程序中串行化部分,程序性能不會隨著并行線程數(shù)目的提升而不斷提升;
?、?嵌入式多核處理器相對于PC處理器而言,其總線速度較慢,并且緩存(Cache)更小,會造成大量數(shù)據(jù)在內(nèi)存(Memory)和緩存(Cache)問不斷拷貝,因此在進行并行化優(yōu)化的過程中,應(yīng)考慮緩存友好性(Cache friendly);
?、?程序并行化執(zhí)行線程數(shù)目應(yīng)
1756-ENBT,A-B,1756-ENBT:李
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