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>> How wide is a typical cache line?
>
>
> Warp said 32 bytes. I thought that was way smaller than I remembered,
> but I went and variously tracked it down, and indeed, most of the modern
> machines seem to have 32-byte cache lines. I think they used to be
> wider, like 128 bytes, but maybe I'm misremembering, or thinking of
> mainframes, or something.
Right. So just to make sure I understand this... you're saying the cache
is managed in chunks of 32 bytes at a time? Like, if you fetch 1 byte of
data from memory, 32 bytes will be loaded into the least recently used
cache line? (Or whatever the cache policy is.)
Are the cache lines aligned in any sort of way? (I'm wondering if it
grabs 32 bytes at the nearest 32-byte boundary or not.)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Orchid XP v8 wrote:
> Right. So just to make sure I understand this... you're saying the cache
> is managed in chunks of 32 bytes at a time? Like, if you fetch 1 byte of
> data from memory, 32 bytes will be loaded into the least recently used
> cache line? (Or whatever the cache policy is.)
That's how I understand it. I believe it's more accurate to say that the
bus between the memory and the registers is actually 32-bytes wide. I
may be mistaken in that, tho.
> Are the cache lines aligned in any sort of way? (I'm wondering if it
> grabs 32 bytes at the nearest 32-byte boundary or not.)
I'm also pretty certain it is on 32-byte boundaries. Otherwise, the
addressing logic winds up being slower than the time you save caching stuff.
--
Darren New / San Diego, CA, USA (PST)
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Orchid XP v8 <voi### [at] dev null> wrote:
> Right. So just to make sure I understand this... you're saying the cache
> is managed in chunks of 32 bytes at a time? Like, if you fetch 1 byte of
> data from memory, 32 bytes will be loaded into the least recently used
> cache line? (Or whatever the cache policy is.)
> Are the cache lines aligned in any sort of way? (I'm wondering if it
> grabs 32 bytes at the nearest 32-byte boundary or not.)
You should read this article series if you want to know everything there
is to know about memory and cache:
http://lwn.net/Articles/250967/
--
- Warp
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