What's a "snoop filter"?

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Thread: What's a "snoop filter"?

  1. #1
    Hammerhead Shark
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    What's a "snoop filter"?

    In laymans terms please

  2. #2
    Crash Test Dummy SkyDog's Avatar
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    The term "snoop filter" is already beyond layman's terms.

    In multiprocessor systems there are multiple L2 caches. A snoop filter keeps tabs on the coherency state of each of those so that each cache controller doesn't need to listen to (or "snoop") the other cache controllers' coherency traffic. Basically, it does the job from a central location so that you don't have a bunch of cache controllers taking up processors' FSB bandwidth with their coherency checking traffic.

  3. #3
    Great White Shark Thermo's Avatar
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    "All mankind is divided into three classes: those that are immovable, those that are movable, and those that move."
    January 21, 2013 The End of an ERROR

  4. #4
    Hammerhead Shark
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    Quote Originally Posted by SkyDog
    The term "snoop filter" is already beyond layman's terms.

    In multiprocessor systems there are multiple L2 caches. A snoop filter keeps tabs on the coherency state of each of those so that each cache controller doesn't need to listen to (or "snoop") the other cache controllers' coherency traffic. Basically, it does the job from a central location so that you don't have a bunch of cache controllers taking up processors' FSB bandwidth with their coherency checking traffic.
    Thanks, SkyDog. I've run across that term repeatedly in Anandtech server/workstation articles. Sounds similar to what used to be known as a "crossbar" circuit in server multiprocessor mainboards, back before multicore processors. It seems interesting to me how cache coherency is maintained in multicore multiprocessor systems, for example a dual 4-core Xeon system. I don't know how the cache are shared or treated as 2 sets of 4, or 8 separate, or whatever. Practically speaking, I suppose it doesn't really matter as long as it works.

  5. #5
    Hammerhead Shark
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    Quote Originally Posted by Thermo
    On the one hand, that article proves SkyDogs' point that "The term "snoop filter" is already beyond layman's terms." lol
    On the other, it helped me build on SkyDogs' description of the term, and was a good jumping-off point to a lot of Googling on the subject. From what I've read so far, effective cache management is going to be a very important aspect of future computer architecture as companies move to massively multicore desktop systems in the future. Intel is already showing off an 80-core x86 type system, and projecting 120-core chips in the relatively near future.

  6. #6
    Tiger Shark linoleum's Avatar
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    Snoop filter for the layman?

    This is one:
    http://www.foxreno.com/news/11404747/detail.html

    and here is another:
    http://feed.insnews.org/v-cgi/feeds....ory_id=2878204


    Sorry, I think that every time I see this topic (and it's been on the front page for awhile now).

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