512GB pages?

Posted May 24, 2023 17:42 UTC (Wed) by willy (subscriber, #9762)
In reply to: 512GB pages? by farnz
Parent article: Memory passthrough for virtual machines

I'm not surprised you don't have I-cache 1GB TLB entries -- do you have any programs with 1GB text segments? Here's my i7-1165G7's TLB configuration:

TLB info
L1 Instruction TLB: 4KB pages, 8-way associative, 128 entries
L1 Instruction TLB: 4MB/2MB pages, 8-way associative, 16 entries
L1 Store Only TLB: 1GB/4MB/2MB/4KB pages, fully associative, 16 entries
L1 Load Only TLB: 4KB pages, 4-way associative, 64 entries
L1 Load Only TLB: 4MB/2MB pages, 4-way associative, 32 entries
L1 Load Only TLB: 1GB pages, fully associative, 8 entries
L2 Unified TLB: 4MB/2MB/4KB pages, 8-way associative, 1024 entries
L2 Unified TLB: 1GB/4KB pages, 8-way associative, 1024 entries

If we did construct a 1GB executable and figure out a way to get it into a 1GB page, and use a PUD entry to map it, that 1GB translation would go into the L2 Unified TLB. The CPU would then create 2MB TLB entries for the L1 cache to use for whichever 2MB chunks of that 1GB executable are actually in use.

If that proved to be a performance problem, I'm pretty sure Intel would figure out they were leaving performance on the table and support 1GB L1 I$ TLB entries.