As from last lecture, we see that increasing the cache line size (which would reduce the M term and reduce the storage overhead) may result in an increase in cache misses due to false sharing (see lecture 11, slide 9), increasing overall interconnect traffic (see lecture 11, slide 11).
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kayvonf
@bstan, great post. To clarify it, I'd like to add that you just gave two different reasons why it might not be good to increase cache line size: (1) potentially more misses due to false sharing and (2) potentially higher bandwidth requirements (to memory and thus on the interconnect). I want to make sure one does not interpret your post as saying that misses might go up, and thus you'll see increased traffic if that is the case. A program can experience higher traffic (e.g., have higher memory BW requirements) with increasing line size even if the total number of misses goes down. This is because with the large lines it is less likely that all the data in a line is actually used by the program, and thus extra data is transferred. In other words, with increasing line size a program must have increasingly high spatial locality in order to avoid transferring unnecessary data.
As from last lecture, we see that increasing the cache line size (which would reduce the M term and reduce the storage overhead) may result in an increase in cache misses due to false sharing (see lecture 11, slide 9), increasing overall interconnect traffic (see lecture 11, slide 11).
This comment was marked helpful 2 times.
@bstan, great post. To clarify it, I'd like to add that you just gave two different reasons why it might not be good to increase cache line size: (1) potentially more misses due to false sharing and (2) potentially higher bandwidth requirements (to memory and thus on the interconnect). I want to make sure one does not interpret your post as saying that misses might go up, and thus you'll see increased traffic if that is the case. A program can experience higher traffic (e.g., have higher memory BW requirements) with increasing line size even if the total number of misses goes down. This is because with the large lines it is less likely that all the data in a line is actually used by the program, and thus extra data is transferred. In other words, with increasing line size a program must have increasingly high spatial locality in order to avoid transferring unnecessary data.
This comment was marked helpful 2 times.