15 213 The course that gives CMU its Zip Memory System Case Studies Mar 20 2008 Topics P6 address translation x86 64 extensions Linux memory management Linux page fault handling Memory mapping class17 ppt Intel P6 Bob Colwell s Chip CMU Alumni Internal designation for successor to Pentium Which had internal designation P5 Fundamentally different from Pentium Out of order superscalar operation Resulting processors Pentium Pro 1996 Pentium II 1997 L2 cache on same chip Pentium III 1999 The freshwater fish machines Saltwater fish machines Pentium 4 Different operation but similar memory system Abandoned by Intel in 2005 for P6 based Core 2 Duo 2 15 213 S 08 P6 Memory System 32 bit address space 4 KB page size L1 L2 and TLBs 4 way set associative DRAM Inst TLB external system bus e g PCI 32 entries 8 sets Data TLB L2 cache 64 entries 16 sets cache bus bus interface unit instruction fetch unit L1 i cache L1 i cache and d cache inst TLB data TLB L1 d cache 16 KB 32 B line size 128 sets L2 cache unified 128 KB 2 MB processor package 3 15 213 S 08 Review of Abbreviations Symbols Components of the virtual address VA Components of the physical address PA 4 TLBI TLB index TLBT TLB tag VPO virtual page offset VPN virtual page number PPO physical page offset same as VPO PPN physical page number CO byte offset within cache line CI cache index CT cache tag 15 213 S 08 Overview of P6 Address Translation 32 result CPU 20 VPN 12 virtual address VA VPO TLB 16 sets 4 entries set 20 PPN PDE 5 L1 128 sets 4 lines set TLB hit 10 10 VPN1 VPN2 PDBR L1 miss L1 hit 16 4 TLBT TLBI TLB miss L2 and DRAM PTE 20 CT 12 PPO 7 5 CI CO physical address PA Page tables 15 213 S 08 P6 2 level Page Table Structure Page directory 1024 4 byte page directory entries PDEs that point to page tables One page directory per process Page directory must be in memory page when its process is running directory Always pointed to by PDBR 1024 Page tables 1024 4 byte page table entries PTEs that point to pages Page tables can be paged in and out 6 PDEs Up to 1024 page tables 1024 PTEs 1024 PTEs 1024 PTEs 15 213 S 08 P6 Page Directory Entry PDE 31 12 11 Page table physical base addr 9 Avail 8 7 G PS 6 5 A 4 3 2 1 0 CD WT U S R W P 1 Page table physical base address 20 most significant bits of physical page table address forces page tables to be 4KB aligned Avail These bits available for system programmers G global page don t evict from TLB on task switch PS page size 4K 0 or 4M 1 A accessed set by MMU on reads and writes cleared by software CD cache disabled 1 or enabled 0 WT write through or write back cache policy for this page table U S user or supervisor mode access R W read only or read write access P page table is present in memory 1 or not 0 31 1 Available for OS page table location in secondary storage 7 0 P 0 15 213 S 08 P6 Page Table Entry PTE 31 12 11 Page physical base address 9 Avail 8 7 6 5 G 0 D A 4 3 2 1 0 CD WT U S R W P 1 Page base address 20 most significant bits of physical page address forces pages to be 4 KB aligned Avail available for system programmers G global page don t evict from TLB on task switch D dirty set by MMU on writes A accessed set by MMU on reads and writes CD cache disabled or enabled WT write through or write back cache policy for this page U S user supervisor R W read write P page is present in physical memory 1 or not 0 31 1 Available for OS page location in secondary storage 8 0 P 0 15 213 S 08 How P6 Page Tables Map Virtual Addresses to Physical Ones 10 VPN1 10 VPN2 word offset into page directory 12 VPO page table PTE PDE PDBR physical address of page directory physical address of page table base if P 1 20 PPN 9 word offset into physical and virtual page word offset into page table page directory Virtual address physical address of page base if P 1 12 PPO Physical address 15 213 S 08 Representation of VM Address Space PT 3 Page Directory P 1 P 1 P 0 P 0 M 1 M 1 M 0 M 1 PT 2 PT 0 P 1 P 0 P 1 P 0 M 1 M 0 M 1 M 1 P 1 P 0 P 1 P 0 M 1 M 0 M 1 M 1 P 0 P 0 P 0 P 0 M 1 M 1 M 0 M 0 Simplified Example 16 page virtual address space Page 15 Page 14 Page 13 Page 12 Page 11 Page 10 Page 9 Page 8 Page 7 Page 6 Page 5 Page 4 Mem Addr Page 3 Disk Addr Page 2 Flags P Is entry in physical memory M Has this part of VA space been mapped 10 In Mem Page 1 Page 0 On Disk Unmapped 15 213 S 08 P6 TLB TLB entry not all documented so this is speculative 20 16 1 1 1 1 1 PPN Tag V G S W D V indicates a valid 1 or invalid 0 TLB entry Tag disambiguates entries cached in the same set PPN translation of the address indicated by index tag G page is global according to PDE PTE S page is supervisor only according to PDE PTE W page is writable according to PDE PTE D PTE has already been marked dirty once is enough Structure of the data TLB 12 entry entry entry entry entry entry 16 sets 4 entries set entry entry entry entry set 0 set 1 entry entry set 15 15 213 S 08 Translating with the P6 TLB 1 Partition VPN into TLBT and TLBI CPU 20 VPN 16 4 TLBT TLBI TLB miss 2 Is the PTE for VPN cached in set TLBI 12 virtual address VPO 1 3 Yes then check 2 PDE page table translation TL PTE B hit permissions build physical address 3 20 PPN 12 PPO physical address 4 No then read PTE and PDE if not cached from memory and build physical address 4 13 15 213 S 08 Translating with the P6 Page Tables case 1 1 20 VPN 12 VPO 20 PPN VPN1 VPN2 12 PPO Case 1 1 page table and page present MMU Action Mem PDE p 1 PTE p 1 data Page directory Page table Data page PDBR OS action Disk 15 MMU builds physical address and fetches data word None 15 213 S 08 Translating with the P6 Page Tables case 1 0 Case 1 0 page table 20 VPN …
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