Hi Carsten Thank you for your comments concerning computer architecture. I feared that the problem will lie there, but simply could not believe in that big difference. In the PC world 10x speed difference means 5 yrs older machine.
> When you then take the m515 with it's Motorola 68K processor - there's NO FPU There are no FP operations involved - int DCT is used. > (another fact: the 'official' JPEG decoding source has in my opinion a too much > overhead.. you may write your own image compression code based on > DCT->quantization->compression of the quantized output(Huffman + RLE or LZ77) I improved a few places but the net gain was small. Overhead you mention does not impact the speed. I analyzed the bottlenecks using MS VC++ profiler on a PC. Major consumers are written very effectivelly. (I am quite sure that any gains here would require using assembler.) I would like to profile on the Palm, but don't know how to do it. (I don't expect that emulator profiling would provide more relevant results. Or am I wrong?) Jan Slodicka ----- Original Message ----- From: "Carsten Koeckritz" <[EMAIL PROTECTED]> Newsgroups: palm-dev-forum To: "Palm Developer Forum" <[EMAIL PROTECTED]> Sent: Thursday, January 09, 2003 12:28 PM Subject: Re: How fast is the Palm? > Jan Slodicka wrote: > > > I recently compared the speed of an identical algorithm (loading a JPEG) on > > several platforms - PC (1.6 MHz), Win CE (about 400 MHz, I forgot now the > > device type but it should not matter) and Palm m515. The results really > > surprised me. > > > > m515 run the program (approx.) 1000x slower than the PC whereas the > > processor speed differs by a factor 50 only. > > CE machine was only 2 times slower than the processor speed difference would > > suggest. > > > > In other words, after linear compensation for different processor speeds CE > > machine seems to be 10 times "faster" than Palm. > > This is for me incredibly bad result for Palm. Naturally I tried to find > > some excuses. > > > > As far as I know devices running WinCE have a RISC-alike processor WITH a FPU. > When you then take the m515 with it's Motorola 68K processor - there's NO FPU > unit - well, there is software floating point support by some libraries ... > but, ahemmm. no comment. :) > Furthermore the 68K (and it's derivates, like the Dragonball in 'earlier' Palm > PDAs (like the m515) ) is a CISC processor - with an ~10 times slower > clockfreq. compared to the devices running WinCE. Plus no cache at all in the > 68K (I don't know about the Dragonball 68K clone - but I'm quite sure it > doesn't have a cache too) > Therefore - if you compile a JPEG decoder with the DCT decoding using floating > point math ... surprise surprise . . . software FPU emulation is for sure > A LOT slower than on a processor using a hardware FPU. > (Even DCT decoding using int-math is much much more powerful on a RISC type > processor (like the ARM), because of it's powerful instruction set (just look > at ARM: multiply AND accumulate in just 1 instruction... mla Rd,Rs1,Rs2,Rs3 > (Rd:= Rs1*Rs2 + Rs3) ... simply wonderful! :) ... not to speak about the > barrel shifter.. ALL registers are general purpose registers ... etc. etc. > ) ahh yes.. just forgot about the instruction pipelining on RISC processor > too... > (another fact: the 'official' JPEG decoding source has in my opinion a too much > overhead.. you may write your own image compression code based on > DCT->quantization->compression of the quantized output(Huffman + RLE or LZ77) > > > After all, comparing the Dragonball 68K devices to ARM (or any other RISC > processor) driven PDAs is like comparing apples with bananas. > (plus: comparing just the processor speeds is senseless too.. just image a > 1000MHz proc. with a Bus-width of 1 bit ;) and then compare the results to > a proc. of 8MHz with a 32 bit wide Bus ... :) > > [don't know if all facts are true.. but I hope it helped a bit. ;) ] > > > Best regards, > Carsten. > > > > > well.. > http://userpages.umbc.edu/~zding1/cmsc611/report.pdf > compares RISC - CISC (not very extensive) > > http://www.ecs.umass.edu/ece/wolf/papers/npw2002.pdf > (although it's about Network-processors it's quite interesting has some > important formulas about processor architecture) > (and you can easily recognize in this paper that a processor isn't just > measured by it's clock frequency) > > ... you should also look for some papers by the gurus of processor > architecture: Hennesy & Patterson > > > > > -- > For information on using the Palm Developer Forums, or to unsubscribe, please see http://www.palmos.com/dev/support/forums/ -- For information on using the Palm Developer Forums, or to unsubscribe, please see http://www.palmos.com/dev/support/forums/
