patch-2.3.43 linux/arch/ia64/lib/copy_page.S

• Lines: 88
• Date: Sun Feb 6 18:42:40 2000
• Orig file: v2.3.42/linux/arch/ia64/lib/copy_page.S
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.3.42/linux/arch/ia64/lib/copy_page.S linux/arch/ia64/lib/copy_page.S
@@ -0,0 +1,87 @@
+/*
+ *
+ * Optimized version of the standard copy_page() function
+ *
+ * Based on comments from ddd. Try not to overflow write buffer.
+ * 
+ * Inputs:
+ * 	in0:	address of target page
+ *	in1:	address of source page
+ * Output:
+ * 	no return value
+ *
+ * Copyright (C) 1999 Hewlett-Packard Co
+ * Copyright (C) 1999 Stephane Eranian <eranian@hpl.hp.com>
+ */
+#include <asm/page.h>
+
+#define lcount		r16
+#define saved_pr	r17
+#define saved_lc	r18
+#define saved_pfs	r19
+#define src1		r20
+#define src2		r21
+#define tgt1		r22
+#define tgt2		r23
+
+	.text
+	.psr abi64
+	.psr lsb
+	.lsb
+
+	.align 32
+	.global copy_page
+	.proc copy_page
+
+copy_page:
+	alloc saved_pfs=ar.pfs,10,0,0,8	// we need 6 roatating (8 minimum)
+					// + 2 input
+
+	.rotr t1[4], t2[4]	// our 2 pipelines with depth of 4 each
+
+	mov saved_lc=ar.lc	// save ar.lc ahead of time
+	mov saved_pr=pr		// rotating predicates are preserved
+				// resgisters we must save.
+	mov src1=in1		// initialize 1st stream source 
+	adds src2=8,in1		// initialize 2nd stream source 
+	mov lcount=PAGE_SIZE/16-1 // as many 16bytes as there are on a page
+				  // -1 is because br.ctop is repeat/until
+
+	adds tgt2=8,in0		// initialize 2nd stream target
+	mov tgt1=in0		// initialize 1st stream target
+	;;
+	mov pr.rot=1<<16	// pr16=1 & pr[17-63]=0 , 63 not modified
+
+	mov ar.lc=lcount	// set loop counter
+	mov ar.ec=4		// ar.ec must match pipeline depth
+	;;
+
+	// We need to preload the n-1 stages of the pipeline (n=depth).
+	// We do this during the "prolog" of the loop: we execute
+	// n-1 times the "load" bundle. Then both loads & stores are
+	// enabled until we reach the end of the last word of the page
+	// on the load side. Then, we enter the epilogue (controlled by ec)
+	// where we just do the stores and no loads n-1 times : drain the pipe.
+	//
+	// The initialization of the prolog is done via the predicate registers:
+	// the choice of pr19 DEPENDS on the depth of the pipeline (n).
+	// When lc > 0 pr63=1 and it is fed back into pr16 and pr16-pr62 
+	// are then shifted right at every iteration,
+	// Thus by initializing pr16=1 and pr17-19=0 (19=16+4-1) before the loop
+	// we get pr19=1 after 4 iterations (n in our case).
+	//
+1:				// engage loop now, let the magic happen...
+(p16)	ld8 t1[0]=[src1],16	// new data on top of pipeline in 1st stream
+(p16)	ld8 t2[0]=[src2],16	// new data on top of pipeline in 2nd stream
+	nop.i 0x0
+(p19)	st8 [tgt1]=t1[3],16	// store top of  1st pipeline
+(p19)	st8 [tgt2]=t2[3],16	// store top of 2nd pipeline
+	br.ctop.dptk.few 1b	// once lc==0, ec-- & p16=0
+				// stores but no loads anymore
+	;;
+	mov pr=saved_pr,0xffffffffffff0000	// restore predicates
+	mov ar.pfs=saved_pfs	// restore ar.ec 
+	mov ar.lc=saved_lc	// restore saved lc
+	br.ret.sptk.few rp	// bye...
+
+	.endp copy_page