tlb

Consider the following loop: .loop: add rsi, STRIDE mov eax, dword [rsi] dec ebp jg .loop where STRIDE is some non-negative integer and rsi contains a pointer to a buffer defined in the bss section. This loop is the only loop in the code. That is, it's not being initialized or touched before the loop. On Linux, all of the 4K virtual pages of the buffer will be mapped on-demand to the same physical page. I've ran this code for all possible strides in the range 0-8192. The measured number of minor and major page faults is exactly 1 and 0, respectively, per page accessed. I've also measured all

The wiki webpage( https://en.wikipedia.org/wiki/Sandy_Bridge ) mentioned that Data TLB has 64, 32 and 4 entries respectively for 4KB, 2MB and 1GB pages. I found these numbers hard to understand. Sandy Bridge has a virtual address of 48 bits, which means for 4K page, there can be 2^36 pages, and for 2MB and 1GB pages, there should be 2^27 and 2^18 pages. If TLB has 64 entries for 4K page, the size of each entry should be no less than 6+36 = 42 bits. Why are there only 32 entries for 2M page, instead of 2^15 (42-27) entries? I know in TLB entries there will be additional bits for control purpose

for (int i = 0; i < 100000; ++i) { int *page = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); page[0] = 0; munmap(page, PAGE_SIZE); } I expect to get ~100000 dTLB-store-misses in userspace, one per each iteration (Also ~100000 page-faults and dTLB-load-misses for kernel). Running following command, the result is roughly 2x what I expect. I would appreciate if someone could clarify why this is the case: perf stat -e dTLB-store-misses:u ./test Performance counter stats for './test': 200,114 dTLB-store-misses 0.213379649 seconds time elapsed P.S. I have

The title might be more specific than my actual problem is, although I believe answering this question would solve a more general problem, which is: how to decrease the effect of high latency (~700 cycle) that comes from random (but coalesced) global memory access in GPUs. In general if one accesses the global memory with coalesced load (eg. I read 128 consecutive bytes), but with very large distance (256KB-64MB) between coalesced accesses, one gets a high TLB (Translation Lookaside Buffer) miss rate. This high TLB miss rate is due to the limited number (~512) and size (~4KB) of the memory

I have been running some benchmarks on some algorithms and profiling their memory usage and efficiency (L1/L2/TLB accesses and misses), and some of the results are quite intriguing for me. Considering an inclusive cache hierarchy (L1 and L2 caches), shouldn't the number of L1 cache misses coincide with the number of L2 cache accesses ? One of the explanations I find would be TLB related: when a virtual address is not mapped in TLB, the system automatically skips searches in some cache levels. Does this seem legitimate? First, inclusive cache hierarchies may not be so common as you assume. For

This is a paragraph from Operating System Concepts, 9th edition by Silberschatz et al: The percentage of times that the page number of interest is found in the TLB is called the hit ratio. An 80-percent hit ratio, for example, means that we find the desired page number in the TLB 80 percent of the time. If it takes 100 nanoseconds to access memory, then a mapped-memory access takes 100 nanoseconds when the page number is in the TLB. If we fail to find the page number in the TLB then we must first access memory for the page table and frame number (100 nanoseconds) and then access the desired