kernel memory checks on boot vs. boot time

[Alexander Best]

On Wed Mar 23 11, Oliver Fromme wrote:
> Bjoern A. Zeeb <bz at freebsd.org> wrote:
>  > as part of the i386/pc98/amd64 boot process we are doing some basic
>  > memory testing, mapping pages and running a couple of pattern
>  > write/read tests on the first bytes (see getmemsize() implmentations).
>  > [...]
>  > With the growing number of memory this can lead to a significant
>  > fraction of kernel startup time on amd64 (~40s delays observed with
>  > 96G of RAM).  Looping over the pages, but not mapping them and not
>  > running the pattern tests reduces this significantly (to single digit
>  > numbers of seconds).
>  > [...]
>  > Not wanting to remove them but maybe make more use of them in the
>  > future (as we do not report any problems we find currently) I'd suggest
>  > to introduce a tunable to disable/enable them, say
>  > 
>  >         hw.run_memtest
> 
> +1 for introducing a tunable.
> 
> I have also noticed the boot delay on server machines with
> lots of memory (all of them are amd64, FWIW).  Co-workers
> have noticed it, too, causing some funny remarks.  :-)

or how about we dump the current memory checks, introduce a tunable and
implement some *real* memory checks. as john pointed out the current checks
are just rudimentary.

> 
> By the way, "big" servers are not the only machines affected.
> I have recently built a small HTPC based on an Atom 330
> (it supports amd64) with 4 GB RAM.  Unfortunately, suspend +
> resume doesn't work, so I have to shutdown and boot it fully
> each time I want to use it.  Needless to say, I would like
> to squeeze every second from the boot process.  Currently,
> the time between the transition from bootloader to kernel
> and the start of init(8) is by far the largest slice of the
> total boot time.

just as a side note: booting a kernel directly from boot stage 2 is broken on
amd64. :( so there's no way around using the boot loader, which will cost extra
time (even with autoboot_delay=0).

so was the adbility to boot a kernel directly from boot2 abandoned? i heard
reports it still works under i386. dunno about the other archs.

cheers.
alex

> 
> Best regards
>    Oliver
> 
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