[U-Boot] [PATCH] arm: Use optimized memcpy and memset from linux

[Wolfgang Denk]

Dear =?ISO-8859-1?Q?Matthias_Wei=DFer?=,

In message <4D3DD1EC.7010506 at arcor.de> you wrote:
>
> >> C version:
> >>    text    data     bss     dec     hex filename
> >>  202862   18912  266456  488230   77326 u-boot
> >>
> >> ASM version:
> >>    text    data     bss     dec     hex filename
> >>  203798   18912  266288  488998   77626 u-boot
> > 
> > How exactly did you measure the speed improvement?
> 
> I inserted a printf before and after calls to these functions with sizes
> of 1MB or more each. I then measured the times between these printfs
> using grabserial (http://elinux.org/Grabserial). In both cases caches
> where enabled.
> 
> To be precise: As memset test case I used the memset(.., 0, ..) of the
> malloc pool (which was 4MB in my case) and a memcpy from flash to RAM
> which I inserted in cmd_bootm.c of about 2.2MB (see RFC patch
> http://patchwork.ozlabs.org/patch/79480/ for exact location of the memcpy).

OK - so which results do you see in reallife use, say when loading and
booting an OS? How much boot time can be saved?

> Do you think a factor of 2 is not possible against the C version? Maybe
> I have done something wrong while measuring theses times. From my point
> of view it should be possible to get such improvements as the code takes
> cache alignment into account and also uses the PLD instruction.

I don;t doubt your measurements.  But this being an optimization
approach, it seems appropriate to check wether we are really
optimizing a hot spot, and if the measured results can be generalized.

I guess the speed improvemnt you see for a few large copy operations
is just one side - probably there will be slower excution (due to the
effort to set up the operations) for the (many more frequent) small
operations.  In addition, there is an increase of the memory footprint
of nearly 1 kB.

I think additional measuremnts need to be done - for example, we
should check how the execution times change for typical operations
like TFTP download, reading from NAND flash and MMC/SDcard, booting a
Linux kernel etc.

Also, it should be possible to enable this feature consditionally, so
users can decide wether speed or size is more important in their
configurations.

> I can do some additional measurements tomorrow on two systems (jadecpu
> with a 32Bit at 166MHz DDR2 memory and a imx25 based on with 16Bit at 133MHz
> LPDDR) and come up with some exact numbers. Maybe you can give some more
> hints what and how the improvements of this patch can be measured.

See above.

Thanks.

Wolfgang Denk

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