Re: [PATCH v5 2/4] powerpc/64: enhance memcmp() with VMX instruction for long bytes comparision
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2018-05-24 07:44:34
Hi Simon, wei.guo.simon@gmail.com writes:
From: Simon Guo <redacted> This patch add VMX primitives to do memcmp() in case the compare size exceeds 4K bytes. KSM feature can benefit from this.
You say "exceeds 4K" here.
quoted hunk ↗ jump to hunk
diff --git a/arch/powerpc/lib/memcmp_64.S b/arch/powerpc/lib/memcmp_64.S index f20e883..6303bbf 100644 --- a/arch/powerpc/lib/memcmp_64.S +++ b/arch/powerpc/lib/memcmp_64.S@@ -27,12 +27,73 @@ #define LH lhbrx #define LW lwbrx #define LD ldbrx +#define LVS lvsr +#define VPERM(_VRT,_VRA,_VRB,_VRC) \ + vperm _VRT,_VRB,_VRA,_VRC #else #define LH lhzx #define LW lwzx #define LD ldx +#define LVS lvsl +#define VPERM(_VRT,_VRA,_VRB,_VRC) \ + vperm _VRT,_VRA,_VRB,_VRC #endif +#define VMX_OPS_THRES 4096
THRES == 4096 BTW, can we call it VMX_THRESH ?
quoted hunk ↗ jump to hunk
+#define ENTER_VMX_OPS \ + mflr r0; \ + std r3,-STACKFRAMESIZE+STK_REG(R31)(r1); \ + std r4,-STACKFRAMESIZE+STK_REG(R30)(r1); \ + std r5,-STACKFRAMESIZE+STK_REG(R29)(r1); \ + std r0,16(r1); \ + stdu r1,-STACKFRAMESIZE(r1); \ + bl enter_vmx_ops; \ + cmpwi cr1,r3,0; \ + ld r0,STACKFRAMESIZE+16(r1); \ + ld r3,STK_REG(R31)(r1); \ + ld r4,STK_REG(R30)(r1); \ + ld r5,STK_REG(R29)(r1); \ + addi r1,r1,STACKFRAMESIZE; \ + mtlr r0 + +#define EXIT_VMX_OPS \ + mflr r0; \ + std r3,-STACKFRAMESIZE+STK_REG(R31)(r1); \ + std r4,-STACKFRAMESIZE+STK_REG(R30)(r1); \ + std r5,-STACKFRAMESIZE+STK_REG(R29)(r1); \ + std r0,16(r1); \ + stdu r1,-STACKFRAMESIZE(r1); \ + bl exit_vmx_ops; \ + ld r0,STACKFRAMESIZE+16(r1); \ + ld r3,STK_REG(R31)(r1); \ + ld r4,STK_REG(R30)(r1); \ + ld r5,STK_REG(R29)(r1); \ + addi r1,r1,STACKFRAMESIZE; \ + mtlr r0 + +/* + * LD_VSR_CROSS16B load the 2nd 16 bytes for _vaddr which is unaligned with + * 16 bytes boundary and permute the result with the 1st 16 bytes. + + * | y y y y y y y y y y y y y 0 1 2 | 3 4 5 6 7 8 9 a b c d e f z z z | + * ^ ^ ^ + * 0xbbbb10 0xbbbb20 0xbbb30 + * ^ + * _vaddr + * + * + * _vmask is the mask generated by LVS + * _v1st_qw is the 1st aligned QW of current addr which is already loaded. + * for example: 0xyyyyyyyyyyyyy012 for big endian + * _v2nd_qw is the 2nd aligned QW of cur _vaddr to be loaded. + * for example: 0x3456789abcdefzzz for big endian + * The permute result is saved in _v_res. + * for example: 0x0123456789abcdef for big endian. + */ +#define LD_VSR_CROSS16B(_vaddr,_vmask,_v1st_qw,_v2nd_qw,_v_res) \ + lvx _v2nd_qw,_vaddr,off16; \ + VPERM(_v_res,_v1st_qw,_v2nd_qw,_vmask) + /* * There are 2 categories for memcmp: * 1) src/dst has the same offset to the 8 bytes boundary. The handlers@@ -174,6 +235,13 @@ _GLOBAL(memcmp) blr .Llong: +#ifdef CONFIG_ALTIVEC + /* Try to use vmx loop if length is larger than 4K */ + cmpldi cr6,r5,VMX_OPS_THRES + bge cr6,.Lsameoffset_vmx_cmp
Here we compare the length to 4K and if it's greater *or equal* then we go to the VMX case. Or am I reading it backward? So we should say "if the size is 4K or more we do VMX" shouldn't we? cheers