Re: [PATCH 6/9] powerpc32: optimise a few instructions in csum_partial()
Le 23/10/2015 05:30, Scott Wood a écrit : On Tue, 2015-09-22 at 16:34 +0200, Christophe Leroy wrote: r5 does contain the value to be updated, so lets use r5 all way long for that. It makes the code more readable. To avoid confusion, it is better to use adde instead of addc The first addition is useless. Its only purpose is to clear carry. As r4 is a signed int that is always positive, this can be done by using srawi instead of srwi Let's also remove the comment about bdnz having no overhead as it is not correct on all powerpc, at least on MPC8xx In the last part, in our situation, the remaining quantity of bytes to be proceeded is between 0 and 3. Therefore, we can base that part on the value of bit 31 and bit 30 of r4 instead of anding r4 with 3 then proceding on comparisons and substractions. Signed-off-by: Christophe Leroy --- arch/powerpc/lib/checksum_32.S | 37 + 1 file changed, 17 insertions(+), 20 deletions(-) Do you have benchmarks for these optimizations? -Scott Using mftbl() to get timebase just before and after call to csum_partial(), I get the following on an MPC885: * 78 bytes packets: 9% faster (11,5 to 10,4 tb ticks) * 328 bytes packets: 3% faster (47,9 to 46,5 tb ticks) Christophe diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S index 3472372..9c12602 100644 --- a/arch/powerpc/lib/checksum_32.S +++ b/arch/powerpc/lib/checksum_32.S @@ -27,35 +27,32 @@ * csum_partial(buff, len, sum) */ _GLOBAL(csum_partial) - addic r0,r5,0 subir3,r3,4 - srwi. r6,r4,2 + srawi. r6,r4,2 /* Divide len by 4 and also clear carry */ beq 3f /* if we're doing < 4 bytes */ - andi. r5,r3,2 /* Align buffer to longword boundary */ + andi. r0,r3,2 /* Align buffer to longword boundary */ beq+1f - lhz r5,4(r3)/* do 2 bytes to get aligned */ - addir3,r3,2 + lhz r0,4(r3)/* do 2 bytes to get aligned */ subir4,r4,2 - addcr0,r0,r5 + addir3,r3,2 srwi. r6,r4,2 /* # words to do */ + adder5,r5,r0 beq 3f 1: mtctr r6 -2: lwzur5,4(r3)/* the bdnz has zero overhead, so it should */ - adder0,r0,r5/* be unnecessary to unroll this loop */ +2: lwzur0,4(r3) + adder5,r5,r0 bdnz2b - andi. r4,r4,3 -3: cmpwi 0,r4,2 - blt+4f - lhz r5,4(r3) +3: andi. r0,r4,2 + beq+4f + lhz r0,4(r3) addir3,r3,2 - subir4,r4,2 - adder0,r0,r5 -4: cmpwi 0,r4,1 - bne+5f - lbz r5,4(r3) - slwir5,r5,8 /* Upper byte of word */ - adder0,r0,r5 -5: addze r3,r0 /* add in final carry */ + adder5,r5,r0 +4: andi. r0,r4,1 + beq+5f + lbz r0,4(r3) + slwir0,r0,8 /* Upper byte of word */ + adder5,r5,r0 +5: addze r3,r5 /* add in final carry */ blr /*
Re: [PATCH 6/9] powerpc32: optimise a few instructions in csum_partial()
On Tue, 2015-09-22 at 16:34 +0200, Christophe Leroy wrote: > r5 does contain the value to be updated, so lets use r5 all way long > for that. It makes the code more readable. > > To avoid confusion, it is better to use adde instead of addc > > The first addition is useless. Its only purpose is to clear carry. > As r4 is a signed int that is always positive, this can be done by > using srawi instead of srwi > > Let's also remove the comment about bdnz having no overhead as it > is not correct on all powerpc, at least on MPC8xx > > In the last part, in our situation, the remaining quantity of bytes > to be proceeded is between 0 and 3. Therefore, we can base that part > on the value of bit 31 and bit 30 of r4 instead of anding r4 with 3 > then proceding on comparisons and substractions. > > Signed-off-by: Christophe Leroy > --- > arch/powerpc/lib/checksum_32.S | 37 + > 1 file changed, 17 insertions(+), 20 deletions(-) Do you have benchmarks for these optimizations? -Scott > > diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S > index 3472372..9c12602 100644 > --- a/arch/powerpc/lib/checksum_32.S > +++ b/arch/powerpc/lib/checksum_32.S > @@ -27,35 +27,32 @@ > * csum_partial(buff, len, sum) > */ > _GLOBAL(csum_partial) > - addic r0,r5,0 > subir3,r3,4 > - srwi. r6,r4,2 > + srawi. r6,r4,2 /* Divide len by 4 and also clear carry */ > beq 3f /* if we're doing < 4 bytes */ > - andi. r5,r3,2 /* Align buffer to longword boundary */ > + andi. r0,r3,2 /* Align buffer to longword boundary */ > beq+1f > - lhz r5,4(r3)/* do 2 bytes to get aligned */ > - addir3,r3,2 > + lhz r0,4(r3)/* do 2 bytes to get aligned */ > subir4,r4,2 > - addcr0,r0,r5 > + addir3,r3,2 > srwi. r6,r4,2 /* # words to do */ > + adder5,r5,r0 > beq 3f > 1: mtctr r6 > -2: lwzur5,4(r3)/* the bdnz has zero overhead, so it should */ > - adder0,r0,r5/* be unnecessary to unroll this loop */ > +2: lwzur0,4(r3) > + adder5,r5,r0 > bdnz2b > - andi. r4,r4,3 > -3: cmpwi 0,r4,2 > - blt+4f > - lhz r5,4(r3) > +3: andi. r0,r4,2 > + beq+4f > + lhz r0,4(r3) > addir3,r3,2 > - subir4,r4,2 > - adder0,r0,r5 > -4: cmpwi 0,r4,1 > - bne+5f > - lbz r5,4(r3) > - slwir5,r5,8 /* Upper byte of word */ > - adder0,r0,r5 > -5: addze r3,r0 /* add in final carry */ > + adder5,r5,r0 > +4: andi. r0,r4,1 > + beq+5f > + lbz r0,4(r3) > + slwir0,r0,8 /* Upper byte of word */ > + adder5,r5,r0 > +5: addze r3,r5 /* add in final carry */ > blr > > /* -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
