lkml.org 
[lkml]   [2004]   [Jul]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] preset loops_per_jiffy for faster booting
On Fri, Jul 09, 2004 at 05:20:07PM -0700, Tim Bird wrote:
> Adam Kropelin wrote:
> > crashes due to a bogus preset. The only problem I can think of with
> > this approach is if there is a system out there so slow that lpj=0 is
> > actually a valid setting.
> It's hard to imagine this case, but that would merely result in
> a calibration, right? For a machine that slow, calibrating the
> delay is the least of their worries. :-)

Good point. ;)

> > be a problem. Perhaps this is worth mentioning in the help text as well.
> I hadn't considered this. (Too much "embedded" on the brain.)
> By help text, do you mean the config text, or something on the wiki page,
> or some other file (in Documentation?).

I meant the config text.

> On the subject of help text, is there a Documentation file I should modify
> or someone I should notify about the addition of a new kernel command line
> option?

Indeed, there is: Documentation/kernel-parameters.txt. You're right; we
should update it.

> > While we're on the topic: Should FASTBOOT perhaps depend on EMBEDDED? I
> > can imagine a user with a massively MP system perhaps finding this
> > option useful, so maybe not.
>
> I had it there originally, then changed my mind. I know some server
> guys are interested in fastboot. This particular change might not
> be that interesting, but some of the other changes we are thinking of
> might not be specific to just embedded.

Ok, let's leave it as-is, then.

> I will do some runtime testing on your patch, but I probably won't be
> able to report back until Monday.

I've made an updated patch below that incorporates the items we just
discussed as well as a couple of things Andreas Dilger sent to me
privately.

> Thanks very much!

No problem. This was a nice little self-contained project to play with
this evening.


Signed-off-by: Adam Kropelin <akropel1@rochester.rr.com>

--- linux-2.6.7/init/main.c.orig Mon Jun 21 17:55:09 2004
+++ linux-2.6.7/init/main.c Fri Jul 9 21:07:44 2004
@@ -167,6 +167,15 @@
return 0;
}

+static unsigned long preset_lpj = CONFIG_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);
@@ -183,40 +192,49 @@
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)... ");
+ } 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;
+ }
+
+ /* 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;
+ }
+
+ /* Round the value and print it */
+ printk("%lu.%02lu BogoMIPS\n",
+ loops_per_jiffy/(500000/HZ),
+ (loops_per_jiffy/(5000/HZ)) % 100);
+ printk("Set 'Preset loops_per_jiffy'=%lu for preset lpj.\n",
+ loops_per_jiffy);

- 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);
- 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\n",
- loops_per_jiffy/(500000/HZ),
- (loops_per_jiffy/(5000/HZ)) % 100);
}

static int __init debug_kernel(char *str)
--- linux-2.6.7/init/Kconfig.orig Mon Jun 21 17:55:09 2004
+++ linux-2.6.7/init/Kconfig Fri Jul 9 21:12:21 2004
@@ -218,6 +218,44 @@
This option enables access to kernel configuration file and build
information through /proc/config.gz.

+menuconfig FASTBOOT
+ bool "Fast boot options"
+ help
+ Say Y here to select among various options that can decrease
+ kernel boot time. These options commonly involve providing
+ hardcoded values for some parameters that the kernel usually
+ determines automatically.
+
+ This option is useful primarily on embedded systems.
+
+ If unsure, say N.
+
+config PRESET_LPJ
+ int "Preset loops_per_jiffy" if FASTBOOT
+ default 0
+ help
+ This is the number of loops used by delay() to achieve a single
+ jiffy of delay inside the kernel. It is normally calculated at
+ boot time, but that calculation can take up to 250 ms per CPU.
+ Specifying a constant value here will eliminate that delay.
+
+ loops_per_jiffy is roughly BogoMips * 5000. To determine the correct
+ value for your kernel, first turn off the fast booting option,
+ compile and boot the kernel on your target hardware, then see what
+ value is printed during the kernel boot. Use that value here.
+
+ A value of 0 results in the normal autodetect behavior at boot.
+
+ The kernel command line parameter "lpj=" can be used to override
+ the value configured here.
+
+ Note that on SMP systems the preset will be applied to all CPUs
+ which will cause problems if for some reason your CPUs need
+ significantly divergent settings.
+
+ If unsure, set this to 0. An incorrect value will cause delays in
+ the kernel to be incorrect. Although unlikely, in the extreme case
+ this might damage your hardware.

menuconfig EMBEDDED
bool "Configure standard kernel features (for small systems)"
--- linux-2.6.7/Documentation/kernel-parameters.txt.orig Fri Jul 9 21:20:16 2004
+++ linux-2.6.7/Documentation/kernel-parameters.txt Fri Jul 9 21:17:11 2004
@@ -576,6 +576,12 @@
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.
+ 0 enables autodetection (default). See Kconfig help text
+ for PRESET_LPJ for details.
+
ltpc= [NET]
Format: <io>,<irq>,<dma>

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2005-03-22 14:04    [W:0.121 / U:3.172 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site