Computing sum introduces true data dependency, e.g. ADDC(sum, t0) ADDC(sum, t1) ADDC(sum, t2) ADDC(sum, t3) Here, each ADDC(sum, ...) references the sum value updated by previous ADDC. In this patch, above sequence is adjusted as following: ADDC(t0, t1) ADDC(t2, t3) ADDC(sum, t0) ADDC(sum, t2) The first two ADDC operations are independent, hence can be executed simultaneously if possible. This patch improves instruction level parallelism, and brings at most 50% csum performance gain on Loongson 3a processor[1]. --- 1. The result can be found at http://dev.lemote.com/files/upload/software/csum-opti/csum-opti-benchmark.html And is generated by a userspace test program: http://dev.lemote.com/files/upload/software/csum-opti/csum-test.tar.gz [v2: amend commit message] arch/mips/lib/csum_partial.S | 38 +++++++++++++++++++------------------- 1 file changed, 19 insertions(+), 19 deletions(-) diff --git a/arch/mips/lib/csum_partial.S b/arch/mips/lib/csum_partial.S index 9901237..6cea101 100644 --- a/arch/mips/lib/csum_partial.S +++ b/arch/mips/lib/csum_partial.S @@ -76,10 +76,10 @@ LOAD _t1, (offset + UNIT(1))(src); \ LOAD _t2, (offset + UNIT(2))(src); \ LOAD _t3, (offset + UNIT(3))(src); \ + ADDC(_t0, _t1); \ + ADDC(_t2, _t3); \ ADDC(sum, _t0); \ - ADDC(sum, _t1); \ - ADDC(sum, _t2); \ - ADDC(sum, _t3) + ADDC(sum, _t2) #ifdef USE_DOUBLE #define CSUM_BIGCHUNK(src, offset, sum, _t0, _t1, _t2, _t3) \ @@ -501,21 +501,21 @@ LEAF(csum_partial) SUB len, len, 8*NBYTES ADD src, src, 8*NBYTES STORE(t0, UNIT(0)(dst), .Ls_exc\@) - ADDC(sum, t0) + ADDC(t0, t1) STORE(t1, UNIT(1)(dst), .Ls_exc\@) - ADDC(sum, t1) + ADDC(sum, t0) STORE(t2, UNIT(2)(dst), .Ls_exc\@) - ADDC(sum, t2) + ADDC(t2, t3) STORE(t3, UNIT(3)(dst), .Ls_exc\@) - ADDC(sum, t3) + ADDC(sum, t2) STORE(t4, UNIT(4)(dst), .Ls_exc\@) - ADDC(sum, t4) + ADDC(t4, t5) STORE(t5, UNIT(5)(dst), .Ls_exc\@) - ADDC(sum, t5) + ADDC(sum, t4) STORE(t6, UNIT(6)(dst), .Ls_exc\@) - ADDC(sum, t6) + ADDC(t6, t7) STORE(t7, UNIT(7)(dst), .Ls_exc\@) - ADDC(sum, t7) + ADDC(sum, t6) .set reorder /* DADDI_WAR */ ADD dst, dst, 8*NBYTES bgez len, 1b @@ -541,13 +541,13 @@ LEAF(csum_partial) SUB len, len, 4*NBYTES ADD src, src, 4*NBYTES STORE(t0, UNIT(0)(dst), .Ls_exc\@) - ADDC(sum, t0) + ADDC(t0, t1) STORE(t1, UNIT(1)(dst), .Ls_exc\@) - ADDC(sum, t1) + ADDC(sum, t0) STORE(t2, UNIT(2)(dst), .Ls_exc\@) - ADDC(sum, t2) + ADDC(t2, t3) STORE(t3, UNIT(3)(dst), .Ls_exc\@) - ADDC(sum, t3) + ADDC(sum, t2) .set reorder /* DADDI_WAR */ ADD dst, dst, 4*NBYTES beqz len, .Ldone\@ @@ -646,13 +646,13 @@ LEAF(csum_partial) nop # improves slotting #endif STORE(t0, UNIT(0)(dst), .Ls_exc\@) - ADDC(sum, t0) + ADDC(t0, t1) STORE(t1, UNIT(1)(dst), .Ls_exc\@) - ADDC(sum, t1) + ADDC(sum, t0) STORE(t2, UNIT(2)(dst), .Ls_exc\@) - ADDC(sum, t2) + ADDC(t2, t3) STORE(t3, UNIT(3)(dst), .Ls_exc\@) - ADDC(sum, t3) + ADDC(sum, t2) .set reorder /* DADDI_WAR */ ADD dst, dst, 4*NBYTES bne len, rem, 1b -- 1.9.0
