[U-Boot] During boot is U-Boot doing its jobs sequentially or in parallel?

[Frank Ihle]

>In message <53283CA4020000460004BF9D at gwia2.rz.hs-offenburg.de> you wrote:
>> 
>> I realized a behavior of U-Boot, which isn't quiet clear to me. I
>> have an ARM9 SAM9G25, that has this boot sequence: AT91Bootstrap ->
>> U-Boot 2010.06 -> Linux 2.6.39. With that system I did 4 Test series
>> about silencing the U-Boot output:
>
>Q1: why are you using so old software?

Because of some patches it's a big job to switch to a newer one.

>Q2: Do you actually have a plan for your optimizations, or are you
    >just poking around at random?

It's not poking around, the aim is to see what effects do some options really ("atomically") have. I'm doing many measurements and always compared with a Buildroot defconfig that takes time around 10.6 s time from Bootloader to Userland.

>> - An image with U-Boot output, without network support in U-Boot - takes about 10.6 s to boot.
>> - An image like above, but without U-Boot output - takes about 10.4 s to boot.
>> --> 200 ms gained
>
>I think it makes little sense to optimize the small parts - like some
>200 ms here - when you appear to ignore the big chunks: a total of 10
>seconds appears to be way too much.  Did you a profiling of the boot
>process, so you can really focus on the big fish?

As mentioned above this is just one options of many I've tried, I already managed to boot the system in about 3-4 s (which now should be even less after I removed some further options). I know the "silent" option is more like out of a option group that gains the last 10 % of speed.

>> Now why is it, when I disable the output, the time stays the same
>> with network support, but around 200 ms are saved without the
>> network? One thing that comes to my mind U-Boot doing its jobs in
>> parallel, is that true? Since there's a waiting when initializing the
>> network there's enough time to do the output ?
>
>We cannot comment on this, as we have no idea what your tests actually
>are, and what exactly you mean by "with or without network support".
>the general rule is that U-Boot is strictly single-tasking, i. e.
>there are no actions running in parallel.

I understand, well this is not a problem, I just like to explain the behavior. In case of interest here is how the network is enabled with the following commands

#define CONFIG_MACB            1
#define CONFIG_RMII            1
#define CONFIG_NET_MULTI        1
#define CONFIG_NET_RETRY_COUNT        20
#define CONFIG_RESET_PHY_R        1

and is disabled with removing the lines above and setting

#undef CONFIG_CMD_NET

>If you are interested in short boot times you should look into using
>the SPL with Falcon mode instead.  Heiko Schocher has some patches in
>the works to do this for the AT91SAM9G20 - here we do not need any
>Atmel code any more; we boot directly into SPL. So you could use
>Falcon mode and load Linux directly from the SPL.

That sounds interesting, I'll search the Internet about this, thanks for the advice.

>But of course none of this is present with an ancient v2010.06
>U-Boot...

Yes, then it would be another reason to double up the almost 4 years of U-Boot development.


Kind Regards

Frank