powerpc: Optimise 64bit csum_partial_copy_generic and add csum_and_copy_from_user

We use the same core loop as the new csum_partial, adding in the
stores and exception handling code. To keep things simple we do all the
exception fixup in csum_and_copy_from_user. This wrapper function is
modelled on the generic checksum code and is careful to always calculate
a complete checksum even if we only copied part of the data to userspace.

To test this I forced checksumming on over loopback and ran socklib (a
simple TCP benchmark). On a POWER6 575 throughput improved by 19% with
this patch. If I forced both the sender and receiver onto the same cpu
(with the hope of shifting the benchmark from being cache bandwidth limited
to cpu limited), adding this patch improved performance by 55%

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 202 insertions, 87 deletions

diff --git a/arch/powerpc/lib/checksum_64.S b/arch/powerpc/lib/checksum_64.S
index 404d5a6e3387..18245af38aea 100644
--- a/arch/powerpc/lib/checksum_64.S
+++ b/arch/powerpc/lib/checksum_64.S
@@ -228,115 +228,230 @@ _GLOBAL(csum_partial)
         srdi    r3,r3,32
         blr
 
+
+        .macro source
+100:
+        .section __ex_table,"a"
+        .align 3
+        .llong 100b,.Lsrc_error
+        .previous
+        .endm
+
+        .macro dest
+200:
+        .section __ex_table,"a"
+        .align 3
+        .llong 200b,.Ldest_error
+        .previous
+        .endm
+
 /*
  * Computes the checksum of a memory block at src, length len,
  * and adds in "sum" (32-bit), while copying the block to dst.
  * If an access exception occurs on src or dst, it stores -EFAULT
- * to *src_err or *dst_err respectively, and (for an error on
- * src) zeroes the rest of dst.
- *
- * This code needs to be reworked to take advantage of 64 bit sum+copy.
- * However, due to tokenring halfword alignment problems this will be very
- * tricky.  For now we'll leave it until we instrument it somehow.
+ * to *src_err or *dst_err respectively. The caller must take any action
+ * required in this case (zeroing memory, recalculating partial checksum etc).
  *
  * csum_partial_copy_generic(r3=src, r4=dst, r5=len, r6=sum, r7=src_err, r8=dst_err)
  */
 _GLOBAL(csum_partial_copy_generic)
-        addic   r0,r6,0
-        subi    r3,r3,4
-        subi    r4,r4,4
-        srwi.   r6,r5,2
-        beq     3f              /* if we're doing < 4 bytes */
-        andi.   r9,r4,2         /* Align dst to longword boundary */
-        beq+    1f
-81:     lhz     r6,4(r3)        /* do 2 bytes to get aligned */
-        addi    r3,r3,2
+        addic   r0,r6,0                 /* clear carry */
+
+        srdi.   r6,r5,3                 /* less than 8 bytes? */
+        beq     .Lcopy_tail_word
+
+        /*
+         * If only halfword aligned, align to a double word. Since odd
+         * aligned addresses should be rare and they would require more
+         * work to calculate the correct checksum, we ignore that case
+         * and take the potential slowdown of unaligned loads.
+         *
+         * If the source and destination are relatively unaligned we only
+         * align the source. This keeps things simple.
+         */
+        rldicl. r6,r3,64-1,64-2         /* r6 = (r3 & 0x3) >> 1 */
+        beq     .Lcopy_aligned
+
+        li      r7,4
+        sub     r6,r7,r6
+        mtctr   r6
+
+1:
+source; lhz     r6,0(r3)                /* align to doubleword */
         subi    r5,r5,2
-91:     sth     r6,4(r4)
-        addi    r4,r4,2
-        addc    r0,r0,r6
-        srwi.   r6,r5,2         /* # words to do */
-        beq     3f
-1:      mtctr   r6
-82:     lwzu    r6,4(r3)        /* the bdnz has zero overhead, so it should */
-92:     stwu    r6,4(r4)        /* be unnecessary to unroll this loop */
-        adde    r0,r0,r6
-        bdnz    82b
-        andi.   r5,r5,3
-3:      cmpwi   0,r5,2
-        blt+    4f
-83:     lhz     r6,4(r3)
         addi    r3,r3,2
-        subi    r5,r5,2
-93:     sth     r6,4(r4)
+        adde    r0,r0,r6
+dest;   sth     r6,0(r4)
         addi    r4,r4,2
+        bdnz    1b
+
+.Lcopy_aligned:
+        /*
+         * We unroll the loop such that each iteration is 64 bytes with an
+         * entry and exit limb of 64 bytes, meaning a minimum size of
+         * 128 bytes.
+         */
+        srdi.   r6,r5,7
+        beq     .Lcopy_tail_doublewords         /* len < 128 */
+
+        srdi    r6,r5,6
+        subi    r6,r6,1
+        mtctr   r6
+
+        stdu    r1,-STACKFRAMESIZE(r1)
+        std     r14,STK_REG(r14)(r1)
+        std     r15,STK_REG(r15)(r1)
+        std     r16,STK_REG(r16)(r1)
+
+source; ld      r6,0(r3)
+source; ld      r9,8(r3)
+
+source; ld      r10,16(r3)
+source; ld      r11,24(r3)
+
+        /*
+         * On POWER6 and POWER7 back to back addes take 2 cycles because of
+         * the XER dependency. This means the fastest this loop can go is
+         * 16 cycles per iteration. The scheduling of the loop below has
+         * been shown to hit this on both POWER6 and POWER7.
+         */
+        .align 5
+2:
+        adde    r0,r0,r6
+source; ld      r12,32(r3)
+source; ld      r14,40(r3)
+
+        adde    r0,r0,r9
+source; ld      r15,48(r3)
+source; ld      r16,56(r3)
+        addi    r3,r3,64
+
+        adde    r0,r0,r10
+dest;   std     r6,0(r4)
+dest;   std     r9,8(r4)
+
+        adde    r0,r0,r11
+dest;   std     r10,16(r4)
+dest;   std     r11,24(r4)
+
+        adde    r0,r0,r12
+dest;   std     r12,32(r4)
+dest;   std     r14,40(r4)
+
+        adde    r0,r0,r14
+dest;   std     r15,48(r4)
+dest;   std     r16,56(r4)
+        addi    r4,r4,64
+
+        adde    r0,r0,r15
+source; ld      r6,0(r3)
+source; ld      r9,8(r3)
+
+        adde    r0,r0,r16
+source; ld      r10,16(r3)
+source; ld      r11,24(r3)
+        bdnz    2b
+
+
         adde    r0,r0,r6
-4:      cmpwi   0,r5,1
-        bne+    5f
-84:     lbz     r6,4(r3)
-94:     stb     r6,4(r4)
-        slwi    r6,r6,8         /* Upper byte of word */
+source; ld      r12,32(r3)
+source; ld      r14,40(r3)
+
+        adde    r0,r0,r9
+source; ld      r15,48(r3)
+source; ld      r16,56(r3)
+        addi    r3,r3,64
+
+        adde    r0,r0,r10
+dest;   std     r6,0(r4)
+dest;   std     r9,8(r4)
+
+        adde    r0,r0,r11
+dest;   std     r10,16(r4)
+dest;   std     r11,24(r4)
+
+        adde    r0,r0,r12
+dest;   std     r12,32(r4)
+dest;   std     r14,40(r4)
+
+        adde    r0,r0,r14
+dest;   std     r15,48(r4)
+dest;   std     r16,56(r4)
+        addi    r4,r4,64
+
+        adde    r0,r0,r15
+        adde    r0,r0,r16
+
+        ld      r14,STK_REG(r14)(r1)
+        ld      r15,STK_REG(r15)(r1)
+        ld      r16,STK_REG(r16)(r1)
+        addi    r1,r1,STACKFRAMESIZE
+
+        andi.   r5,r5,63
+
+.Lcopy_tail_doublewords:                /* Up to 127 bytes to go */
+        srdi.   r6,r5,3
+        beq     .Lcopy_tail_word
+
+        mtctr   r6
+3:
+source; ld      r6,0(r3)
+        addi    r3,r3,8
         adde    r0,r0,r6
-5:      addze   r3,r0           /* add in final carry (unlikely with 64-bit regs) */
-        rldicl  r4,r3,32,0      /* fold 64 bit value */
-        add     r3,r4,r3
-        srdi    r3,r3,32
-        blr
+dest;   std     r6,0(r4)
+        addi    r4,r4,8
+        bdnz    3b
 
-/* These shouldn't go in the fixup section, since that would
-   cause the ex_table addresses to get out of order. */
+        andi.   r5,r5,7
 
-        .globl src_error_1
-src_error_1:
-        li      r6,0
-        subi    r5,r5,2
-95:     sth     r6,4(r4)
+.Lcopy_tail_word:                       /* Up to 7 bytes to go */
+        srdi.   r6,r5,2
+        beq     .Lcopy_tail_halfword
+
+source; lwz     r6,0(r3)
+        addi    r3,r3,4
+        adde    r0,r0,r6
+dest;   stw     r6,0(r4)
+        addi    r4,r4,4
+        subi    r5,r5,4
+
+.Lcopy_tail_halfword:                   /* Up to 3 bytes to go */
+        srdi.   r6,r5,1
+        beq     .Lcopy_tail_byte
+
+source; lhz     r6,0(r3)
+        addi    r3,r3,2
+        adde    r0,r0,r6
+dest;   sth     r6,0(r4)
         addi    r4,r4,2
-        srwi.   r6,r5,2
-        beq     3f
-        mtctr   r6
-        .globl src_error_2
-src_error_2:
-        li      r6,0
-96:     stwu    r6,4(r4)
-        bdnz    96b
-3:      andi.   r5,r5,3
-        beq     src_error
-        .globl src_error_3
-src_error_3:
-        li      r6,0
-        mtctr   r5
-        addi    r4,r4,3
-97:     stbu    r6,1(r4)
-        bdnz    97b
-        .globl src_error
-src_error:
+        subi    r5,r5,2
+
+.Lcopy_tail_byte:                       /* Up to 1 byte to go */
+        andi.   r6,r5,1
+        beq     .Lcopy_finish
+
+source; lbz     r6,0(r3)
+        sldi    r9,r6,8                 /* Pad the byte out to 16 bits */
+        adde    r0,r0,r9
+dest;   stb     r6,0(r4)
+
+.Lcopy_finish:
+        addze   r0,r0                   /* add in final carry */
+        rldicl  r4,r0,32,0              /* fold two 32 bit halves together */
+        add     r3,r4,r0
+        srdi    r3,r3,32
+        blr
+
+.Lsrc_error:
         cmpdi   0,r7,0
-        beq     1f
+        beqlr
         li      r6,-EFAULT
         stw     r6,0(r7)
-1:      addze   r3,r0
         blr
 
-        .globl dst_error
-dst_error:
+.Ldest_error:
         cmpdi   0,r8,0
-        beq     1f
+        beqlr
         li      r6,-EFAULT
         stw     r6,0(r8)
-1:      addze   r3,r0
         blr
-
-.section __ex_table,"a"
-        .align  3
-        .llong  81b,src_error_1
-        .llong  91b,dst_error
-        .llong  82b,src_error_2
-        .llong  92b,dst_error
-        .llong  83b,src_error_3
-        .llong  93b,dst_error
-        .llong  84b,src_error_3
-        .llong  94b,dst_error
-        .llong  95b,dst_error
-        .llong  96b,dst_error
-        .llong  97b,dst_error