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loader: Set twiddle globaldiv to 16 by default

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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>
This commit is contained in:
Colin Percival 2021-09-28 11:39:59 -07:00
parent 667ea7385d
commit 7457840230
5 changed files with 8 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
stand/common/console.c
View File

@ -56,7 +56,7 @@ cons_probe(void)
TSENTER();
/* We want a callback to install the new value when this var changes. */
env_setenv("twiddle_divisor", EV_VOLATILE, "1", twiddle_set,
env_setenv("twiddle_divisor", EV_VOLATILE, "16", twiddle_set,
env_nounset);
/* Do all console probes */

3
stand/defaults/loader.conf
View File

@ -111,7 +111,8 @@ module_blacklist="drm drm2 radeonkms i915kms amdgpu" # Loader module blacklist
#tftp.blksize="1428" # Set the RFC 2348 TFTP block size.
# If the TFTP server does not support RFC 2348,
# the block size is set to 512. Valid: (8,9007)
#twiddle_divisor="1" # >1 means slow down the progress indicator.
#twiddle_divisor="16" # >16 slows down the progress indicator;
# <16 speeds up the progress indicator.
### Kernel settings ########################################
# The following boot_ variables are enabled by setting them to any value.

2
stand/libsa/twiddle.c
View File

@ -42,7 +42,7 @@ __FBSDID("$FreeBSD$");
/* Extra functions from NetBSD standalone printf.c */
static u_int globaldiv;
static u_int globaldiv = 16;
void
twiddle(u_int callerdiv)

3
stand/man/loader.8
View File

@ -644,7 +644,8 @@ Throttles the output of the
I/O progress indicator displayed while loading the kernel and modules.
This is useful on slow serial consoles where the time spent waiting for
these characters to be written can add up to many seconds.
The default is 1 (full speed); a value of 2 spins half as fast, and so on.
The default is 16; a value of 32 spins half as fast,
while a value of 8 spins twice as fast.
.It Va vm.kmem_size
Sets the size of kernel memory (bytes).
This overrides the value determined when the kernel was compiled.

3
stand/man/loader_simp.8
View File

@ -624,7 +624,8 @@ Throttles the output of the
I/O progress indicator displayed while loading the kernel and modules.
This is useful on slow serial consoles where the time spent waiting for
these characters to be written can add up to many seconds.
The default is 1 (full speed); a value of 2 spins half as fast, and so on.
The default is 16; a value of 32 spins half as fast,
while a value of 8 spins twice as fast.
.It Va vm.kmem_size
Sets the size of kernel memory (bytes).
This overrides the value determined when the kernel was compiled.