Booting FreeBSD on an EC2 c5.xlarge instance, the loader "twiddles"
810 times over the course of 510 ms, a rate of 1.59 kHz. Even accepting
that many systems are slower than this particular VM and will take
longer to boot (especially if using spinning-rust disks), this seems
like an unhelpfully large amount of twiddling when compared to the
~60 Hz frame rate of many displays; printing the twiddles also consumes
roughly 10% of the boot time on the aforementioned VM.
Setting the default globaldiv to 16 dramatically reduces the time spent
printing twiddles to the console while still twiddling at roughly 100
Hz; this should be ample even for systems which take longer to boot and
consequently twiddle slower.
Note that this can adjusted via the twiddle_divisor variable in
loader.conf, but that file is not processed until nearly halfway
through the loader's runtime.
Reviewed by: allanjude, jrtc27, kevans
MFC after: 1 week
Sponsored by: https://www.patreon.com/cperciva
Differential Revision: <https://reviews.freebsd.org/D32163>
In my initial testing, these are the functions which showed up as
being worth instrumenting. More may be added later.
common/console.c: cons_probe
common/gfx_fb.c: read_list, insert_font, autoload_font
common/interp.c: interact
common/interp_lua.c: interp_init, interp_run
efi/libefi/efipart.c: efipart_readwrite
i386/libi386/biosdisk.c: bd_init, bd_open, bd_edd_io, bd_chs_io, bd_io
libsa/open.c: open
libsa/read.c: read
libsa/twiddle.c: twiddle
Note that profiling interp_run may be of questionable utility as it
may depend on user behaviour (e.g. pressing keys).
Reviewed by: kevans (earlier version)
