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OldFart
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The Myth of RAM-access Posted on 13-Jan-2024 10:37:27
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Elite Member |
Joined: 12-Sep-2004 Posts: 3060
From: Stad; en d'r is moar ain stad en da's Stad. Makkelk zat! | | |
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| Hi,
A few days ago I was pointed to THIS series (4) of articles. When you posess a proper grasp on math (I, as a bookkeeper of sorts, merely get the gist), you may indulge in it. Have a nice read!
OldFart _________________ More then three levels of indigestion and you're scroomed! |
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Karlos
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Re: The Myth of RAM-access Posted on 13-Jan-2024 10:55:58
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Elite Member |
Joined: 24-Aug-2003 Posts: 4405
From: As-sassin-aaate! As-sassin-aaate! Ooh! We forgot the ammunition! | | |
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| @OldFart
Where's the myth part? We all know that ram accesses tend to transfer entire cache lines, even when asking for a single byte where data cache exists and is enabled and that randomly accessing data over a wide distance (like traversing a linked list with node addresses scattered all over the show) is suboptimal. The best memory performance is achieved generally for streaming sequential operations under such circumstances.
After that you've got additional complications from memory management, paging strategies and so forth. _________________ Doing stupid things for fun... |
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OldFart
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Re: The Myth of RAM-access Posted on 13-Jan-2024 11:20:22
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Elite Member |
Joined: 12-Sep-2004 Posts: 3060
From: Stad; en d'r is moar ain stad en da's Stad. Makkelk zat! | | |
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| @Karlos
Quote:
The myth, as the author clearly states, is, that memoryaccess of the kind he depicts are/were considered to be O(1), whatever that means (remember I'm a bookkeeper!), however he debunks, or tries to debunk that.
From the preface: Quote:
This article is the first of four in a series, in which I argue that thinking of a memory access as O(1) is generally a bad idea, and we should instead think of them as taking O(√N) time. |
Please, don't shoot the messenger!
OldFart_________________ More then three levels of indigestion and you're scroomed! |
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Karlos
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Re: The Myth of RAM-access Posted on 13-Jan-2024 11:27:57
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Elite Member |
Joined: 24-Aug-2003 Posts: 4405
From: As-sassin-aaate! As-sassin-aaate! Ooh! We forgot the ammunition! | | |
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| @OldFart
Not shooting, don't worry. I guess I wasn't sure why even when the article was written any engineers would still think memory accesses were simple things you just counted in basic cycles. That all went out of the window with caches. _________________ Doing stupid things for fun... |
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OneTimer1
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Re: The Myth of RAM-access Posted on 13-Jan-2024 19:49:20
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Cult Member |
Joined: 3-Aug-2015 Posts: 983
From: Unknown | | |
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| Quote:
Karlos wrote:
Where's the myth part? We all know that ram accesses tend to transfer entire cache lines, ...
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Some really don't know or they don't accept the consequences, reading data from continuous addresses is much faster than reading data from a lot of different addresses. The Amiga DMA engine would have needed caches to do the same for higher DMA transfers with the same memory chips. |
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