From: Adam Kropelin <akropel1@rochester.rr.com>
Adds a kernel boot parameter "lpj=NNN" which allows the operator to specify
the loops-per-jiffy value. This shaves up to a quarter of a second off
boot times, which are critical for embedded appliances.
It's a bit thin, but the code is in __init.
Signed-off-by: Adam Kropelin <akropel1@rochester.rr.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/Documentation/kernel-parameters.txt | 14 +++
25-akpm/init/main.c | 111 +++++++++++++++++-----------
2 files changed, 85 insertions(+), 40 deletions(-)
diff -puN Documentation/kernel-parameters.txt~preset-loops_per_jiffy-for-faster-booting Documentation/kernel-parameters.txt
--- 25/Documentation/kernel-parameters.txt~preset-loops_per_jiffy-for-faster-booting 2004-08-15 22:47:55.438417864 -0700
+++ 25-akpm/Documentation/kernel-parameters.txt 2004-08-15 22:47:55.443417104 -0700
@@ -574,6 +574,20 @@ running once the system is up.
so, the driver will manage that printer.
See also header of drivers/char/lp.c.
+ lpj=n [KNL]
+ Sets loops_per_jiffy to given constant, thus avoiding
+ time-consuming boot-time autodetection (up to 250 ms per
+ CPU). 0 enables autodetection (default). To determine
+ the correct value for your kernel, boot with normal
+ autodetection and see what value is printed. Note that
+ on SMP systems the preset will be applied to all CPUs,
+ which is likely to cause problems if your CPUs need
+ significantly divergent settings. An incorrect value
+ will cause delays in the kernel to be wrong, leading to
+ unpredictable I/O errors and other breakage. Although
+ unlikely, in the extreme case this might damage your
+ hardware.
+
ltpc= [NET]
Format: <io>,<irq>,<dma>
diff -puN init/main.c~preset-loops_per_jiffy-for-faster-booting init/main.c
--- 25/init/main.c~preset-loops_per_jiffy-for-faster-booting 2004-08-15 22:47:55.440417560 -0700
+++ 25-akpm/init/main.c 2004-08-15 22:47:55.445416800 -0700
@@ -183,15 +183,28 @@ static int __init obsolete_checksetup(ch
return 0;
}
-/* this should be approx 2 Bo*oMips to start (note initial shift), and will
- still work even if initially too large, it will just take slightly longer */
+static unsigned long preset_lpj;
+static int __init lpj_setup(char *str)
+{
+ preset_lpj = simple_strtoul(str,NULL,0);
+ return 1;
+}
+
+__setup("lpj=", lpj_setup);
+
+/*
+ * This should be approx 2 Bo*oMips to start (note initial shift), and will
+ * still work even if initially too large, it will just take slightly longer
+ */
unsigned long loops_per_jiffy = (1<<12);
EXPORT_SYMBOL(loops_per_jiffy);
-/* This is the number of bits of precision for the loops_per_jiffy. Each
- bit takes on average 1.5/HZ seconds. This (like the original) is a little
- better than 1% */
+/*
+ * This is the number of bits of precision for the loops_per_jiffy. Each
+ * bit takes on average 1.5/HZ seconds. This (like the original) is a little
+ * better than 1%
+ */
#define LPS_PREC 8
void __devinit calibrate_delay(void)
@@ -199,40 +212,53 @@ void __devinit calibrate_delay(void)
unsigned long ticks, loopbit;
int lps_precision = LPS_PREC;
- loops_per_jiffy = (1<<12);
+ if (preset_lpj) {
+ loops_per_jiffy = preset_lpj;
+ printk("Calibrating delay loop (skipped)... "
+ "%lu.%02lu BogoMIPS preset\n",
+ loops_per_jiffy/(500000/HZ),
+ (loops_per_jiffy/(5000/HZ)) % 100);
+ } else {
+ loops_per_jiffy = (1<<12);
- printk("Calibrating delay loop... ");
- while ((loops_per_jiffy <<= 1) != 0) {
- /* wait for "start of" clock tick */
- ticks = jiffies;
- while (ticks == jiffies)
- /* nothing */;
- /* Go .. */
- ticks = jiffies;
- __delay(loops_per_jiffy);
- ticks = jiffies - ticks;
- if (ticks)
- break;
- }
+ printk("Calibrating delay loop... ");
+ while ((loops_per_jiffy <<= 1) != 0) {
+ /* wait for "start of" clock tick */
+ ticks = jiffies;
+ while (ticks == jiffies)
+ /* nothing */;
+ /* Go .. */
+ ticks = jiffies;
+ __delay(loops_per_jiffy);
+ ticks = jiffies - ticks;
+ if (ticks)
+ break;
+ }
+
+ /*
+ * Do a binary approximation to get loops_per_jiffy set to
+ * equal one clock (up to lps_precision bits)
+ */
+ loops_per_jiffy >>= 1;
+ loopbit = loops_per_jiffy;
+ while (lps_precision-- && (loopbit >>= 1)) {
+ loops_per_jiffy |= loopbit;
+ ticks = jiffies;
+ while (ticks == jiffies)
+ /* nothing */;
+ ticks = jiffies;
+ __delay(loops_per_jiffy);
+ if (jiffies != ticks) /* longer than 1 tick */
+ loops_per_jiffy &= ~loopbit;
+ }
-/* Do a binary approximation to get loops_per_jiffy set to equal one clock
- (up to lps_precision bits) */
- loops_per_jiffy >>= 1;
- loopbit = loops_per_jiffy;
- while ( lps_precision-- && (loopbit >>= 1) ) {
- loops_per_jiffy |= loopbit;
- ticks = jiffies;
- while (ticks == jiffies);
- ticks = jiffies;
- __delay(loops_per_jiffy);
- if (jiffies != ticks) /* longer than 1 tick */
- loops_per_jiffy &= ~loopbit;
+ /* Round the value and print it */
+ printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
+ loops_per_jiffy/(500000/HZ),
+ (loops_per_jiffy/(5000/HZ)) % 100,
+ loops_per_jiffy);
}
-/* Round the value and print it */
- printk("%lu.%02lu BogoMIPS\n",
- loops_per_jiffy/(500000/HZ),
- (loops_per_jiffy/(5000/HZ)) % 100);
}
static int __init debug_kernel(char *str)
@@ -254,8 +280,10 @@ static int __init quiet_kernel(char *str
__setup("debug", debug_kernel);
__setup("quiet", quiet_kernel);
-/* Unknown boot options get handed to init, unless they look like
- failed parameters */
+/*
+ * Unknown boot options get handed to init, unless they look like
+ * failed parameters
+ */
static int __init unknown_bootoption(char *param, char *val)
{
/* Change NUL term back to "=", to make "param" the whole string. */
@@ -266,8 +294,10 @@ static int __init unknown_bootoption(cha
if (obsolete_checksetup(param))
return 0;
- /* Preemptive maintenance for "why didn't my mispelled command
- line work?" */
+ /*
+ * Preemptive maintenance for "why didn't my mispelled command
+ * line work?"
+ */
if (strchr(param, '.') && (!val || strchr(param, '.') < val)) {
printk(KERN_ERR "Unknown boot option `%s': ignoring\n", param);
return 0;
@@ -307,7 +337,8 @@ static int __init init_setup(char *str)
unsigned int i;
execute_command = str;
- /* In case LILO is going to boot us with default command line,
+ /*
+ * In case LILO is going to boot us with default command line,
* it prepends "auto" before the whole cmdline which makes
* the shell think it should execute a script with such name.
* So we ignore all arguments entered _before_ init=... [MJ]
_