CPU-> GPU传输与GPU-> CPU传输 [英] CPU->GPU transfer vs GPU->CPU transfer

问题描述

我一直在做一些有关测量从
CPU-> GPU和GPU-> CPU传输数据的延迟的实验。我发现，对于特定消息大小，CPU-> GPU数据传输速率几乎是GPU-> CPU传输速率的两倍。有人可以解释我为什么会这样吗？

I have been doing some experiments regarding measuring the latency of data transfer from CPU->GPU and GPU->CPU. I found that CPU->GPU data transfer rate is almost twice as much compared to GPU->CPU transfer rate for a particular message size. Can anybody explain me why this is so?

推荐答案

由于不了解实验的详细信息，例如CPU / GPU是什么使用过，如何测量传输速率，我只是猜测，从CPU-> GPU进行
数据传输，通常是通过DMA。每次它可以将一个块字节从系统内存传输到图形内存。
但是从GPU-> CPU进行数据传输，通常CPU是读取由PCI总线映射的图形光圈存储器。 CPU仅能以不可缓存的严格顺序逐字节读取光圈存储器，因此速度很慢。

Since don't know the detail about your experiment, like what's CPU/GPU used, how to measure transfer rate, I just guess that, data transfer from CPU->GPU, normally is through DMA. each time it can transfer a block bytes from system memory to graphic memory. But data transfer from GPU->CPU, normally CPU is to read the graphic aperture memory which is mapped by PCI bus. CPU only can read the aperture memory in un-cacheable, strict order byte by byte, so it is slow.

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