diff options
Diffstat (limited to 'cache.inc')
| -rw-r--r-- | cache.inc | 85 |
1 files changed, 59 insertions, 26 deletions
@@ -1,6 +1,6 @@ ; -*- fundamental -*- --------------------------------------------------- ; -; Copyright 2004 H. Peter Anvin - All Rights Reserved +; Copyright 2004-2007 H. Peter Anvin - All Rights Reserved ; ; This program is free software; you can redistribute it and/or modify ; it under the terms of the GNU General Public License as published by @@ -11,17 +11,33 @@ ; ----------------------------------------------------------------------- section .text + + struc cptr +.sector: resd 1 ; Sector number +.prev: resw 1 ; LRU pointer to previous (less recent) +.next: resw 1 ; LRU pointer to next (more recent) + endstruc +cptr_size_lg2 equ 3 + +NCacheEntries equ 65536/SECTOR_SIZE + ; ; initcache: Initialize the cache data structures ; initcache: xor eax,eax ; We don't care about sector 0 mov di,CachePtrs - mov cx,65536/SECTOR_SIZE - rep stosd + mov cx,NCacheEntries+1 + mov bx,CachePtrs+NCacheEntries*cptr_size ; "prev" pointer +.loop: + mov [di+cptr.sector],eax ; Zero sector number + mov [di+cptr.prev],bx ; Previous pointer + mov [bx+cptr.next],di ; Previous entry's next pointer + mov bx,di + add di,cptr_size + loop .loop ret - ; ; getcachesector: Check for a particular sector (EAX) in the sector cache, ; and if it is already there, return a pointer in GS:SI @@ -31,32 +47,29 @@ initcache: ; getcachesector: push cx + push bx + push di mov si,cache_seg mov gs,si - mov si,CachePtrs ; Sector cache pointers - mov cx,65536/SECTOR_SIZE + mov si,CachePtrs+cptr_size ; Real sector cache pointers + mov cx,NCacheEntries .search: cmp eax,[si] jz .hit - add si,4 + add si,cptr_size loop .search .miss: TRACER 'M' - ; Need to load it. Highly inefficient cache replacement - ; algorithm: Least Recently Written (LRW) - push bx + ; Need to load it. push es push gs pop es - mov bx,[NextCacheSlot] - inc bx - and bx,(1 << (16-SECTOR_SHIFT))-1 - mov [NextCacheSlot],bx - shl bx,2 - mov [CachePtrs+bx],eax - shl bx,SECTOR_SHIFT-2 + mov bx,[CachePtrs+cptr.next] ; "Next most recent than head node" + mov [bx+cptr.sector],eax mov si,bx + sub bx,CachePtrs+cptr_size + shl bx,SECTOR_SHIFT-cptr_size_lg2 ; Buffer address pushad %if IS_EXTLINUX call getonesec_ext @@ -65,18 +78,38 @@ getcachesector: %endif popad pop es - pop bx - pop cx - ret - -.hit: ; We have it; get the pointer +.hit: + ; Update LRU, then compute buffer address TRACER 'H' - sub si,CachePtrs - shl si,SECTOR_SHIFT-2 + + ; Remove from current position in the list + mov bx,[si+cptr.prev] + mov di,[si+cptr.next] + mov [bx+cptr.next],di + mov [di+cptr.prev],bx + + ; Add to just before head node + mov bx,[CachePtrs+cptr.prev] + mov [si+cptr.prev],bx + mov [bx+cptr.next],si + mov [CachePtrs+cptr.prev],si + mov word [si+cptr.next],CachePtrs + + sub si,CachePtrs+cptr_size + shl si,SECTOR_SHIFT-cptr_size_lg2 ; Buffer address + + pop di + pop bx pop cx ret section .latebss + + ; Each CachePtr contains: + ; - Block pointer + ; - LRU previous pointer + ; - LRU next pointer + ; The first entry is the head node of the list alignb 4 -CachePtrs resd 65536/SECTOR_SIZE ; Cached sector pointers -NextCacheSlot resw 1 ; Next cache slot to occupy +CachePtrs resb (NCacheEntries+1)*cptr_size + |