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A[10][10]
And assume that the cache line is 10 int's long and also the memory is in row major format. If i try to access A[2][2] then will the whole row A[2] be cached in cache memory ?
5 replies to this topic
#1
Posted 31 December 2011 - 05:01 AM
P98
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Array is
And assume that the cache line is 10 int's long and also the memory is in row major format. If i try to access A[2][2] then will the whole row A[2] be cached in cache memory ?
And assume that the cache line is 10 int's long and also the memory is in row major format. If i try to access A[2][2] then will the whole row A[2] be cached in cache memory ?
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#2
Posted 31 December 2011 - 08:40 AM
AKMafia001
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Nop! It will be only a single cell. i.e. The cell on the intersection of row 2 and column 2.
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#3
Posted 31 December 2011 - 01:54 PM
mebob
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@AKMafia I don't think that was what he was asking.
@P98 Is this a homework question?
@P98 Is this a homework question?
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#4
Posted 31 December 2011 - 07:42 PM
P98
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This is not a homework question. I was just curious to know what happens. Well why isnt the entire row written into the cache ?
#5
Posted 31 December 2011 - 11:20 PM
Alexander
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Array accessors are a convenience. A[2][2] is really something more like *(*(A + 2) + 2) for the sake of memory.
What is "cache"? A[2] is likely in the memory stack if local or memory heap if allocated with something such as malloc, if you call that cache (it is a little ambiguous)
P98 said:
Well why isnt the entire row written into the cache ?
What is "cache"? A[2] is likely in the memory stack if local or memory heap if allocated with something such as malloc, if you call that cache (it is a little ambiguous)
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#6
Posted 02 January 2012 - 01:23 PM
mebob
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By cache do you mean the CPU cache (i.e. L1, L2, L3 caches)?
If you do, that question is very hard to answer. How the caching is done isn't really something they document (publicly at least). It would totally depend on what CPU you are using. If you really want to find an answer, you may want to contact your CPU manufacturer (probably Intel or AMD) and ask them about your particular CPU model.
Aside from that, the cache would probably not cache the entire row, as the CPU has no way of knowing that what you are accessing is a pointer. In fact, a pointer residing in the memory looks exactly the same as, say, an int (on a 32 bit system at least).
If you do, that question is very hard to answer. How the caching is done isn't really something they document (publicly at least). It would totally depend on what CPU you are using. If you really want to find an answer, you may want to contact your CPU manufacturer (probably Intel or AMD) and ask them about your particular CPU model.
Aside from that, the cache would probably not cache the entire row, as the CPU has no way of knowing that what you are accessing is a pointer. In fact, a pointer residing in the memory looks exactly the same as, say, an int (on a 32 bit system at least).
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