Re: Interesting pentium-memcpy results

Michael L. Galbraith (
Mon, 28 Jul 1997 22:43:42 +0200 (MET DST)

On Mon, 28 Jul 1997, Benjamin Saller Bender wrote:

> Chris Evans <> writes:
> >I just compared 2.1.46 vs. 2.1.46+pentium memcpy patch, and interestingly
> >enough found that the UNIX byte benchmarks tended to _drop_ a fair bit,
> >with the exception of process creation and execl throughput. (Note that I
> >only ran the basic 'system' tests - TCP bandwidth etc. to be determined
> >when I find the newer benchmarks)
> >
> >It does however show us that there still is performance to be gained. I
> >presume the process creation test will be using fork() which does a lot of
> >memcpy'ing of various process credentials in kernel space.
> >
> I haven't done the research to verify how well this will work under
> Linux, but for large a memcpy on the P5 we may wanna consider using the FP
> unit using double precision read and writes. I have sample code if anyone is
> interested.
> --
> Benjamin Saller Bender <>
> AppliedTheory Communications Software Engineering Group
> Sentio aliquos togatos contra me conspirare.

I have done a lot of benching with it.. it's a big win here except for X
mostly. There are places where it doesn't win.. ergo why it's not in the
kernel tree?.. but it wins a LOT more than it loses here.