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SubjectRe: memcpy() too slow?
On Fri, 17 Apr 1998, Matthew Wilcox wrote:

> I used my Acorn RiscPC with an ARM610 processor to test. The CPU is clocked

Nice computer...

> at 30MHz and the bus is 32-bits wide at 16MHz. It has no secondary cache
> and 4k of 4-way set-associative first level cache. It took 86 centiseconds
> to copy 16MB of overlapping memory - the start addresses were &4000 and
> &80000, so the chances of data being in the 4k cache were remote. I'm sure
> those with faster or wider busses, EDO RAM or SDRAM and second level caches
> would get better results than I. The typical Pentium has a 64-bit wide
> memory bus, clocked at 33 or 50MHz, so you can divide my timings by 4 or 6
> immediately.
>
> On my machine the speed of pagecpy is 210us/page, plus-or-minus 1us, which
> is approx 5 pages per millisecond. So if a driver wanted a contiguous 32k
> page chunk, it would have to wait 3/5 of a millisecond for it, in the worst
> case. Is this really too slow compared to the extra swapping involved with
> keeping large amounts of free memory?

OK, let's do it... Once Ben and Stephen have finished their
reverse-pte lookup structure.
You can be quite sure that this will be in 2.3.xx
(and in 2.2.xx unofficial patches :)

Rik.
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