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From: Steven Rostedt <rostedt@goodmis.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: paulus@samba.org, linuxppc-dev@ozlabs.org,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] add strncmp to PowerPC
Date: Fri, 29 Feb 2008 22:56:45 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.58.0802292250490.21555@gandalf.stny.rr.com> (raw)
In-Reply-To: <1204340690.15052.457.camel@pasglop>
On Sat, 1 Mar 2008, Benjamin Herrenschmidt wrote:
>
> Do we have any indication that it performs better than the C one ?
See below.
>
> Ben.
>
> >
> > +_GLOBAL(strncmp)
> > + mtctr r5
> > + addi r5,r3,-1
> > + addi r4,r4,-1
> > +1: lbzu r3,1(r5)
> > + cmpwi 1,r3,0
> > + lbzu r0,1(r4)
> > + subf. r3,r0,r3
> > + beqlr 1
> > + bdnzt eq,1b
> > + blr
> > +
And here's the objdump of the C version:
0000000000000080 <.strncmp>:
80: fb e1 ff f0 std r31,-16(r1)
84: f8 21 ff c1 stdu r1,-64(r1)
88: 7c 69 1b 78 mr r9,r3
8c: 7c a0 2b 79 mr. r0,r5
90: 38 60 00 00 li r3,0
94: 7c 09 03 a6 mtctr r0
98: 7c 3f 0b 78 mr r31,r1
9c: 41 82 00 68 beq- 104 <.strncmp+0x84>
a0: 89 69 00 00 lbz r11,0(r9)
a4: 88 04 00 00 lbz r0,0(r4)
a8: 7c 00 58 50 subf r0,r0,r11
ac: 78 00 06 20 clrldi r0,r0,56
b0: 2f a0 00 00 cmpdi cr7,r0,0
b4: 7c 00 07 74 extsb r0,r0
b8: 7c 03 03 78 mr r3,r0
bc: 40 9e 00 48 bne- cr7,104 <.strncmp+0x84>
c0: 2f ab 00 00 cmpdi cr7,r11,0
c4: 41 9e 00 40 beq- cr7,104 <.strncmp+0x84>
c8: 38 84 00 01 addi r4,r4,1
cc: 38 69 00 01 addi r3,r9,1
d0: 42 40 00 30 bdz- 100 <.strncmp+0x80>
d4: 88 03 00 00 lbz r0,0(r3)
d8: 89 24 00 00 lbz r9,0(r4)
dc: 38 63 00 01 addi r3,r3,1
e0: 38 84 00 01 addi r4,r4,1
e4: 2f 20 00 00 cmpdi cr6,r0,0
e8: 7c 09 00 50 subf r0,r9,r0
ec: 78 00 06 20 clrldi r0,r0,56
f0: 2f a0 00 00 cmpdi cr7,r0,0
f4: 7c 00 07 74 extsb r0,r0
f8: 40 9e 00 08 bne- cr7,100 <.strncmp+0x80>
fc: 40 9a ff d4 bne+ cr6,d0 <.strncmp+0x50>
100: 7c 03 03 78 mr r3,r0
104: e8 21 00 00 ld r1,0(r1)
108: eb e1 ff f0 ld r31,-16(r1)
10c: 4e 80 00 20 blr
I'll let you decide ;-)
Even if it was logically faster (which I still doubt) it's a hell of a lot
of cache lines to waste.
-- Steve
next prev parent reply other threads:[~2008-03-01 3:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-29 16:04 [PATCH] add strncmp to PowerPC Steven Rostedt
2008-03-01 3:04 ` Benjamin Herrenschmidt
2008-03-01 3:56 ` Steven Rostedt [this message]
2008-03-03 9:54 ` Gabriel Paubert
2008-03-03 10:10 ` Andreas Schwab
2008-03-03 19:08 ` Segher Boessenkool
2008-03-05 4:03 ` Paul Mackerras
2008-03-05 5:26 ` Segher Boessenkool
2008-03-05 5:39 ` Paul Mackerras
2008-03-05 7:01 ` Segher Boessenkool
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