CODEWITHSUNDEEP
clinuxlinux-kerneldmanetwork-driver
user786
user786

Reputation: 4374

If I create dma mapping then does prefetch function fetches data from the device DMA mapped area and populate area to hold whats read from mapped area

I like to know how linux function prefetch works

It is defined as

    #ifndef ARCH_HAS_PREFETCH
    #define prefetch(x) __builtin_prefetch(x)
    #endif

so in drivers this can be found

        rx_buf = page_address(tp->Rx_databuff[entry]);//Rx_databuff[] are Page type array
        dma_sync_single_for_cpu(d, addr, pkt_size, DMA_FROM_DEVICE);
        prefetch(rx_buf);
        skb_copy_to_linear_data(skb, rx_buf, pkt_size);

So rtl 8139 device has 256 Rx descriptors. and addr parameter to dma_sync_single_for_cpu is I think enables reading from device and save the data in some temporary memory(what is this memory area?) and so prefetch I think is just reading that memory area and populating the rx_buf from that memory area.

I wish I could see __builtin_prefetch(x) defination but I could not find it so what's going on with prefetch call can anyone please tell me this

Upvotes: 0

Views: 101

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