powerpc: Fix POWER7/PPC64 performance regression on LE

This patch fixes a performance regression on the POWER7/PPC64 memcmp porting for Little Endian. The LE code uses 'ldbrx' instruction to read the memory on byte reversed form, however ISA 2.06 just provide the indexed form which uses a register value as additional index, instead of a fixed value enconded in the instruction. And the port strategy for LE uses r0 index value and update the address value on each compare loop interation. For large compare size values, it adds 8 more instructions plus some more depending of trailing size. This patch fixes it by adding pre-calculate indexes to remove the address update on loops and tailing sizes. For large sizes it shows a considerable gain, with double performance pairing with BE.
git-mirror · Jan 13, 2015 · ce6615c · ce6615c
1 parent d3b00f4
commit ce6615c
Show file tree

Hide file tree

Showing 2 changed files with 285 additions and 588 deletions.
diff --git a/ChangeLog b/ChangeLog
@@ -1,5 +1,8 @@
 2015-01-13  Adhemerval Zanella  <azanella@linux.vnet.ibm.com>
 
+	* sysdeps/powerpc/powerpc64/power7/memcmp.S (memcmp): Fix performance
+	regression on LE.
+
 	* sysdeps/powerpc/powerpc64/multiarch/strncmp-power8.S: New file.
 	* sysdeps/powerpc/powerpc64/power8/strncmp.S: New file.
 	* sysdeps/powerpc/powerpc64/multiarch/Makefile [sysdep_routines]: Add