Messages in this thread | | | Date | Fri, 17 Apr 1998 11:21:20 +0200 (MET DST) | From | Rik van Riel <> | Subject | Re: memcpy() too slow? |
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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 :)
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