What is optimum line size in cache?

We find that for high performance microprocessor designs, line sizes in the range 16-64 bytes seem best; shorter line sizes yield high delays due to memory latency, although they reduce memory traffic somewhat. …

How big is a cache line?

The block of memory that is transferred to a memory cache. The cache line is generally fixed in size, typically ranging from 16 to 256 bytes. The effectiveness of the line size depends on the application, and cache circuits may be configurable to a different line size by the system designer.

What is the impact of cache line size on performance?

The cache parameters are based on optimizing overall performance and cost. Increasing the cache line size can have a positive impact on performance. When a program has a high locality of reference (for example walking through a string or array), a long cache line size can improve performance.

Is line size is equal to block size in cache?

Increasing the block size decreases the number of lines in cache. With the increase in block size, the number of bits in block offset increases. However, with the decrease in the number of cache lines, number of bits in line number decreases.

What is the cache line size in words?

Each cache line is 1 word (4 bytes).

How are cache lines calculated?

Each cache line/slot matches a memory block. That means each cache line contains 16 bytes. If the cache is 64Kbytes then 64Kbytes/16 = 4096 cache lines. To address these 4096 cache lines, we need 12 bits (212 = 4096).

Are cache lines always 64 bytes?

A cache line is the unit of data transfer between the cache and main memory . Typically the cache line is 64 bytes. The processor will read or write an entire cache line when any location in the 64 byte region is read or written.

How do I find the cache line?

So for any given byte, the cache line which has to be fetched can be found by clearing the least signficant six bits of the address, which corresponds to rounding down to the nearest address that is divisible by 64. Processors may have multi-level caches (L1, L2, L3), and these differ on size and speed.

How and when to align to cache line size?

The assumption is that each cacheline_pad_t will itself be aligned to a 64 byte (its size) cache line boundary, and hence whatever follows it will be on the next cache line.

How big is a memory page and a cache line?

For most CPUs, page sizes will be at least 4KB and generally support a mix of 4KB/64KB/2MB/4MB/16MB/1GB (not necessarily all supported at the same time). The size will always be a power of two. Both a page and a cache line are contiguous and require to be aligned to their respective size.

Why do you need to align data to memory line size?

In particular, many new instructions require that data must be aligned to 16-byte boundaries. Additionally, by aligning frequently used data to the cache line size of a specific processor, you improve cache performance.

How big is the cache line on x86?

On x86 cache lines are 64 bytes, however, to prevent false sharing, you need to follow the guidelines of the processor you are targeting (intel has some special notes on its netburst based processors), generally you need to align to 64 bytes for this (intel states that you should also avoid crossing 16 byte boundries).