问题
I read a paragraph about DRAM(main memory) cache miss and SRAM(L1,L2,L3) cache miss and I am not sure what it means.
Since DRAM is slower than SRAM, the cost for cache misses is expensive because DRAm cache misses are served from disk, while SRAM cache misses are usually served from DRAM based main memory.
Here is my understanding : if there is a cache miss in DRAM, it goes into disk(second memory) to find datum. while if there is a cache miss in SRAM, it goes into SRAM to find the datum.
Could you tell if I am right or wrong ?
回答1:
In general, if there's a miss at level L, you have to go one level further down, L+1.
A typical memory hierarchy comprises the following levels, from 0 onwards:
- Processor registers
- Processor caches (SRAM)
- System memory (DRAM)
- Mass storage (Flash/Spinning devices)
If you want to store something in a local register, you have to first fetch it from memory.
If your data is in one of the caches of the processor (SRAM), you don't need to go further down. If you have a cache miss however, you have to go to system memory (DRAM).
What happens here is that you might try to access a memory page which is not in memory, either because it has never been loaded or because at some point it has been swapped out. You have a page fault and you need to fetch your page from storage devices. This process stops as soon as you find your data.
Note that you want to avoid as much as possible access to slow storage drives, so what you can do it to create additional caching layers between DRAM and spinning disks by means of faster devices, e.g. SSDs (ZFS L2ARC, bcache etc)
来源：https://stackoverflow.com/questions/29451066/dram-cache-miss