Boot time: Initial main memory initialization optimizations?

Boot time: Initial main memory initialization optimizations?

[Dirk Behme]

Hi,

regarding boot time optimization, on an embedded ARM Cortex-A9 based 
system with 512MB or 1GB main memory, we found that initializing this 
main memory takes a somehow large amount of time.

Initializing 512MB takes <= ~100ms, the additional 512MB on the 1GB 
take <= ~100ms additionally, too. So in sum <= ~200ms for 1GB.

Having a short look to this, it looks like most of the time is spent 
in arch/arm/mm/init.c in 
bootmem_init()/arm_bootmem_init()/arm_bootmem_free().

Has anybody already looked into this if there are any optimizations 
possible? Maybe even some hacks, if the main memory size (512MB/1GB) 
is always known? Any pointers?

I'm looking for reducing (a) the overall init time and maybe (b) the 
dependency on the memory size.

Thanks

Dirk

Re: Boot time: Initial main memory initialization optimizations?

[Rob Landley]

On 05/05/14 10:40, Dirk Behme wrote:
> Hi,
> 
> regarding boot time optimization, on an embedded ARM Cortex-A9 based
> system with 512MB or 1GB main memory, we found that initializing this
> main memory takes a somehow large amount of time.
> 
> Initializing 512MB takes <= ~100ms, the additional 512MB on the 1GB take
> <= ~100ms additionally, too. So in sum <= ~200ms for 1GB.
> 
> Having a short look to this, it looks like most of the time is spent in
> arch/arm/mm/init.c in bootmem_init()/arm_bootmem_init()/arm_bootmem_free().
> 
> Has anybody already looked into this if there are any optimizations
> possible? Maybe even some hacks, if the main memory size (512MB/1GB) is
> always known? Any pointers?

There were a couple of longish threads last year. Random links into the
middle of 'em:

http://www.spinics.net/lists/linux-mm/msg54027.html
http://lkml.iu.edu//hypermail/linux/kernel/1306.3/01915.html

> I'm looking for reducing (a) the overall init time and maybe (b) the
> dependency on the memory size.

Basically they were deferring init by abusing the hotplug mechanism, so
the system started with less memory and a background thread added more
of it.

Rob