Re: tweaking MemSet() performance

Would you please retest this.  I have attached my email showing a
simpler test that is less error-prone.

I can't come up with any scenario that would produce what you have
reported.  If I look at function call cost, MemSet loop efficiency, and
memset loop efficiency, I can't come up with a combination that produces
what you reported.

The standard assumption is that function call overhead is significant,
and that memset it faster than C MemSet.  What compiler are you using?
Is the memset() call being inlined by the compiler?  You will have to
look at the assembler code to be sure.

My only guess is that memset is inlined and that it is only moving
single bytes.  If that is the case, there is no function call overhead
and it would explain why MemSet gets faster as the buffer gets larger.

---------------------------------------------------------------------------

Andrew Sullivan wrote:
> On Thu, Aug 29, 2002 at 01:27:41AM -0400, Neil Conway wrote:
> >
> > Also, if anyone would like to contribute the results of doing the
> > benchmark on their particular system, that might provide some useful
> > additional data points.
>
> Ok, here's a run on a Sun E450, Solaris 7.  I presume your "total"
> time label corresponds to my "real" time.  That's what I'm including,
> anyway.
>
> System Configuration:  Sun Microsystems  sun4u Sun Enterprise 450 (2
> X UltraSPARC-II 400MHz)
> System clock frequency: 100 MHz
> Memory size: 2560 Megabytes
>
> BUFFER_SIZE = 64
>         MemSet(): 0m13.343s,12.567s,13.659s
>         memset(): 0m1.255s,0m1.258s,0m1.254s
>
> BUFFER_SIZE = 128
>         MemSet(): 0m21.347s,0m21.200s,0m20.541s
>         memset(): 0m18.041s,0m17.963s,0m17.990s
>
> BUFFER_SIZE = 256
>         MemSet(): 0m38.023s,0m37.480s,0m37.631s
>         memset(): 0m25.969s,0m26.047s,0m26.012s
>
> BUFFER_SIZE = 512
>         MemSet(): 1m9.226s,1m9.901s,1m10.148s
>         memset(): 2m17.897s,2m18.310s,2m17.984s
>
> BUFFER_SIZE = 1024
>         MemSet(): 2m13.690s,2m13.981s,2m13.206s
>         memset(): 4m43.195s,4m43.405s,4m43.390s
>
> . . .at which point I gave up.
>
> A
>
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> Andrew Sullivan                         204-4141 Yonge Street
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