Peter Marheine submitted this change.
Make sleep threshold for delays configurable
This allows the minimum time that default_delay() will choose to sleep
for instead of polling to be configured at build-time. The default
remains unchanged at 100 milliseconds for now.
The test's correctness has been checked by testing with minimum sleep
time left at its default and set to a non-default value smaller than 100
microseconds (both pass without sleeping, verified with strace) and with
the minimum sleep time set to 0 (causing the test to be skipped). The
configured value from the macro needs to be stored in a const to avoid
-Werror=type-limits errors when configured to be zero.
Change-Id: Ida96e0816ac914ed69d6fd82ad90ebe89cdef1cc
Signed-off-by: Peter Marheine <pmarheine@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/81606
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Anastasia Klimchuk <aklm@chromium.org>
---
M Makefile
M meson.build
M meson_options.txt
M tests/udelay.c
M udelay.c
M udelay_dos.c
6 files changed, 38 insertions(+), 10 deletions(-)
diff --git a/Makefile b/Makefile
index 9b94e22..97f56b8 100644
--- a/Makefile
+++ b/Makefile
@@ -542,6 +542,11 @@
# Disable wiki printing by default. It is only useful if you have wiki access.
CONFIG_PRINT_WIKI ?= no
+# Minimum time in microseconds to suspend execution for (rather than polling)
+# when a delay is required. Larger values may perform better on machines with
+# low timer resolution, at the cost of increased power.
+CONFIG_DELAY_MINIMUM_SLEEP_US ?= 100000
+
# Disable all features if CONFIG_NOTHING=yes is given unless CONFIG_EVERYTHING was also set
ifeq ($(CONFIG_NOTHING), yes)
ifeq ($(CONFIG_EVERYTHING), yes)
@@ -587,6 +592,7 @@
endif
FEATURE_FLAGS += -D'CONFIG_DEFAULT_PROGRAMMER_ARGS="$(CONFIG_DEFAULT_PROGRAMMER_ARGS)"'
+FEATURE_FLAGS += -D'CONFIG_DELAY_MINIMUM_SLEEP_US=$(CONFIG_DELAY_MINIMUM_SLEEP_US)'
################################################################################
diff --git a/meson.build b/meson.build
index c4d7717..458b6e8 100644
--- a/meson.build
+++ b/meson.build
@@ -112,6 +112,9 @@
delay_src = files('udelay_dos.c')
endif
srcs += delay_src
+cargs += ['-DCONFIG_DELAY_MINIMUM_SLEEP_US=@0@'.format(
+ get_option('delay_minimum_sleep_us')
+)]
# check for required symbols
if cc.has_function('clock_gettime')
diff --git a/meson_options.txt b/meson_options.txt
index e62deb6..8a04114 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -22,3 +22,6 @@
option('documentation', type : 'feature', value : 'auto', description : 'build the html documentation')
option('ni845x_search_path', type : 'string', value : 'C:\Program Files (x86)\National Instruments\Ni-845x\MS Visual C',
description : 'Path to search for the proprietary ni845x library and header (32-bit Windows only)')
+option('delay_minimum_sleep_us', type : 'integer', min : 0, value : 100000,
+ description : 'Minimum time in microseconds to suspend execution for (rather than polling) when a delay is required.'
+ + ' Larger values may perform better on machines with low timer resolution, at the cost of increased power.')
diff --git a/tests/udelay.c b/tests/udelay.c
index 277a15d..8d24b00 100644
--- a/tests/udelay.c
+++ b/tests/udelay.c
@@ -34,6 +34,8 @@
#endif
}
+static const int64_t min_sleep = CONFIG_DELAY_MINIMUM_SLEEP_US;
+
/*
* A short delay should delay for at least as long as requested,
* and more than 10x as long would be worrisome.
@@ -43,9 +45,21 @@
* test.
*/
void udelay_test_short(void **state) {
+ /*
+ * Delay for 100 microseconds, or short enough that we won't sleep.
+ * It's not useful to test the sleep path because we assume the OS won't
+ * sleep for less time than we ask.
+ */
+ int64_t delay_us = 100;
+ if (delay_us >= min_sleep)
+ delay_us = min_sleep - 1;
+ /* No point in running this test if delay always sleeps. */
+ if (delay_us <= 0)
+ skip();
+
uint64_t start = now_us();
- default_delay(100);
+ default_delay(delay_us);
uint64_t elapsed = now_us() - start;
- assert_in_range(elapsed, 100, 1000);
+ assert_in_range(elapsed, delay_us, 10 * delay_us);
}
diff --git a/udelay.c b/udelay.c
index 453cb34..c43b6e3 100644
--- a/udelay.c
+++ b/udelay.c
@@ -92,14 +92,15 @@
#endif
}
+static const unsigned min_sleep = CONFIG_DELAY_MINIMUM_SLEEP_US;
+
/* Precise delay. */
void default_delay(unsigned int usecs)
{
- /* If the delay is >0.1 s, use internal_sleep because timing does not need to be so precise. */
- if (usecs > 100000) {
- internal_sleep(usecs);
- } else {
+ if (usecs < min_sleep) {
clock_usec_delay(usecs);
+ } else {
+ internal_sleep(usecs);
}
}
diff --git a/udelay_dos.c b/udelay_dos.c
index 61493fc..c3914ea 100644
--- a/udelay_dos.c
+++ b/udelay_dos.c
@@ -153,19 +153,20 @@
usleep(usecs % 1000000);
}
+static const unsigned min_sleep = CONFIG_DELAY_MINIMUM_SLEEP_US;
+
/* Precise delay. */
void default_delay(unsigned int usecs)
{
static bool calibrated = false;
- /* If the delay is >0.1 s, use internal_sleep because timing does not need to be so precise. */
- if (usecs > 100000) {
- internal_sleep(usecs);
- } else {
+ if (usecs < min_sleep) {
if (!calibrated) {
myusec_calibrate_delay();
calibrated = true;
}
myusec_delay(usecs);
+ } else {
+ internal_sleep(usecs);
}
}
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