MIPS: csum_partial: Improve instruction parallelism. (615eb603) · Commits · 戴 / test

Computing sum introduces true data dependency. This patch removes some true data depdendencies, hence increases instruction level parallelism. This patch brings up to 50% csum performance gain on Loongson 3a. One example about how this patch works is in CSUM_BIGCHUNK1: // ** original ** vs ** patch applied ** ADDC(sum, t0) ADDC(t0, t1) ADDC(sum, t1) ADDC(t2, t3) ADDC(sum, t2) ADDC(sum, t0) ADDC(sum, t3) ADDC(sum, t2) In the original implementation, each ADDC(sum, ...) depends on the sum value updated by previous ADDC(as source operand). With this patch applied, the first two ADDC operations are independent, hence can be executed simultaneously if possible. Another example is in the "copy and sum calculating chunk": // ** original ** vs ** patch applied ** STORE(t0, UNIT(0) ... STORE(t0, UNIT(0) ... ADDC(sum, t0) ADDC(t0, t1) STORE(t1, UNIT(1) ... STORE(t1, UNIT(1) ... ADDC(sum, t1) ADDC(sum, t0) STORE(t2, UNIT(2) ... STORE(t2, UNIT(2) ... ADDC(sum, t2) ADDC(t2, t3) STORE(t3, UNIT(3) ... STORE(t3, UNIT(3) ... ADDC(sum, t3) ADDC(sum, t2) With this patch applied, ADDC and the **next next** ADDC are independent. Signed-off-by:

chenj <chenj@lemote.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/9608/ Signed-off-by:

Ralf Baechle <ralf@linux-mips.org>

arch/mips/lib/csum_partial.S

+19 −19

Original line number	Diff line number	Diff line
		@@ -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) \
		@@ -504,21 +504,21 @@ 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
		@@ -544,13 +544,13 @@ 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\@
		@@ -649,13 +649,13 @@ 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

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