Results 1 to 3 of 3

Thread: using the prefetch command

  1. #1
    Junior Member
    Join Date
    Feb 2010
    Posts
    10

    using the prefetch command

    Greetings,

    I've been trying to use prefetch to improve my performance, but haven't seen any impact one way or another. I wonder if I'm using the command the correct way. I haven't been able to find any code samples that show its correct use.

    My code uses a loop to read chunks of data from global memory into local memory, and then process it. I use a barrier command to synchronize the threads, and an async_work_group_copy() command followed by a wait_group_event to transfer the data to local memory. Right after that, I kick off a prefetch command to the next chunk of global memory, and then process the data in the local memory. I *think* the next time I transfer data to local memory at the top of the loop, it should happen faster, but as I said, I don't see any performance payoff.

    Am I misunderstanding how to use prefetch()? Can anyone point me to the correct usage?

    BTW, I'm using a compute capability 1.1 card.

    Many thanks!

  2. #2
    Senior Member
    Join Date
    Jul 2009
    Location
    Northern Europe
    Posts
    311

    Re: using the prefetch command

    My understanding is that prefetch and async_copy aren't really supported in hardware on most (if any GPUs). They might give great performance on something like a CELL system which has good DMA support. My guess is that prefetch is just a no-op on most systems today and that async_copy does a non-async copy in reality. So I would not expect better performance today, but it might be so in the future.

  3. #3
    Junior Member
    Join Date
    Feb 2010
    Posts
    10

    Re: using the prefetch command

    OK, good to know. It does seem that the async copy does the copy in a coalesced manner -- that's what the profiler says -- but since I have a wait right after it, I've been using it as if it was a synchronous copy.

Similar Threads

  1. Command Queue
    By chanakya.sun in forum OpenCL
    Replies: 3
    Last Post: 11-09-2011, 05:39 PM
  2. Problem with Command queue
    By Gregorien in forum OpenCL
    Replies: 0
    Last Post: 03-25-2010, 02:55 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •