Instruction fetches can be done in chunks with the assumption that much of the time you are going to run through many instructions in a row. so instruction fetches can be more efficient, there is likely a handful or more clocks of overhead per transaction then the delay for the memory to have the data … Read more
volatile only forces your code to re-read the value, it cannot control where the value is read from. If the value was recently read by your code then it will probably be in cache, in which case volatile will force it to be re-read from cache, NOT from memory. There are not a lot of … Read more
L1 is very tightly coupled to the CPU core, and is accessed on every memory access (very frequent). Thus, it needs to return the data really fast (usually within on clock cycle). Latency and throughput (bandwidth) are both performance-critical for L1 data cache. (e.g. four cycle latency, and supporting two reads and one write by … Read more
Fortunately, there is more than one way to explicitly flush the caches. The instruction “wbinvd” writes back modified cache content and marks the caches empty. It executes a bus cycle to make external caches flush their data. Unfortunately, it is a privileged instruction. But if it is possible to run the test program under something … Read more
The important distinction here is between cache misses caused by the size of your data set, and cache misses caused by the way your cache and data alignment are organized. Lets assume you have a 32k direct mapped cache, and consider the following 2 cases: You repeatedly iterate over a 128k array. There’s no way … Read more
It is near impossible to find specs on Intel caches. When I was teaching a class on caches last year, I asked friends inside Intel (in the compiler group) and they couldn’t find specs. But wait!!! Jed, bless his soul, tells us that on Linux systems, you can squeeze lots of information out of the … Read more
This is a complex problem closely related to architectural features of modern processors and your intuition that random read are slower than random writes because the CPU has to wait for the read data is not verified (most of the time). There are several reasons for that I will detail. Modern processors are very efficient … Read more
To answer specifically the headline question: Yes, recent1 mainstream Intel CPUs support non-temporal loads on normal 2 memory – but only “indirectly” via non-temporal prefetch instructions, rather than directly using non-temporal load instructions like movntdqa. This is in contrast to non-temporal stores where you can just use the corresponding non-temporal store instructions3 directly. The basic … Read more
Yes, CPU register is just a small amount of data storage, that facilitates some CPU operations. CPU cache, it is a high speed volatile memory which is bigger in size, that helps the processor to reduce the memory operations.
In a multiprocessor system or a multicore processor (Intel Quad Core, Core two Duo etc..) does each cpu core/processor have its own cache memory (data and program cache)? Yes. It varies by the exact chip model, but the most common design is for each CPU core to have its own private L1 data and instruction … Read more