cpu-load: standardize document format
Each text file under Documentation follows a different format. Some doesn't even have titles! Change its representation to follow the adopted standard, using ReST markups for it to be parseable by Sphinx: - mark literals; - Adjust document title; - Use a list for references. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab
Jonathan Corbet
parent
f68ac62d11
commit
09338fb0f4
1 changed files with 59 additions and 58 deletions
|
|
@ -1,9 +1,10 @@
|
|||
========
|
||||
CPU load
|
||||
--------
|
||||
========
|
||||
|
||||
Linux exports various bits of information via `/proc/stat' and
|
||||
`/proc/uptime' that userland tools, such as top(1), use to calculate
|
||||
the average time system spent in a particular state, for example:
|
||||
Linux exports various bits of information via ``/proc/stat`` and
|
||||
``/proc/uptime`` that userland tools, such as top(1), use to calculate
|
||||
the average time system spent in a particular state, for example::
|
||||
|
||||
$ iostat
|
||||
Linux 2.6.18.3-exp (linmac) 02/20/2007
|
||||
|
|
@ -17,7 +18,7 @@ Here the system thinks that over the default sampling period the
|
|||
system spent 10.01% of the time doing work in user space, 2.92% in the
|
||||
kernel, and was overall 81.63% of the time idle.
|
||||
|
||||
In most cases the `/proc/stat' information reflects the reality quite
|
||||
In most cases the ``/proc/stat`` information reflects the reality quite
|
||||
closely, however due to the nature of how/when the kernel collects
|
||||
this data sometimes it can not be trusted at all.
|
||||
|
||||
|
|
@ -33,78 +34,78 @@ Example
|
|||
-------
|
||||
|
||||
If we imagine the system with one task that periodically burns cycles
|
||||
in the following manner:
|
||||
in the following manner::
|
||||
|
||||
time line between two timer interrupts
|
||||
|--------------------------------------|
|
||||
^ ^
|
||||
|_ something begins working |
|
||||
|_ something goes to sleep
|
||||
(only to be awaken quite soon)
|
||||
time line between two timer interrupts
|
||||
|--------------------------------------|
|
||||
^ ^
|
||||
|_ something begins working |
|
||||
|_ something goes to sleep
|
||||
(only to be awaken quite soon)
|
||||
|
||||
In the above situation the system will be 0% loaded according to the
|
||||
`/proc/stat' (since the timer interrupt will always happen when the
|
||||
``/proc/stat`` (since the timer interrupt will always happen when the
|
||||
system is executing the idle handler), but in reality the load is
|
||||
closer to 99%.
|
||||
|
||||
One can imagine many more situations where this behavior of the kernel
|
||||
will lead to quite erratic information inside `/proc/stat'.
|
||||
will lead to quite erratic information inside ``/proc/stat``::
|
||||
|
||||
|
||||
/* gcc -o hog smallhog.c */
|
||||
#include <time.h>
|
||||
#include <limits.h>
|
||||
#include <signal.h>
|
||||
#include <sys/time.h>
|
||||
#define HIST 10
|
||||
/* gcc -o hog smallhog.c */
|
||||
#include <time.h>
|
||||
#include <limits.h>
|
||||
#include <signal.h>
|
||||
#include <sys/time.h>
|
||||
#define HIST 10
|
||||
|
||||
static volatile sig_atomic_t stop;
|
||||
static volatile sig_atomic_t stop;
|
||||
|
||||
static void sighandler (int signr)
|
||||
{
|
||||
(void) signr;
|
||||
stop = 1;
|
||||
}
|
||||
static unsigned long hog (unsigned long niters)
|
||||
{
|
||||
stop = 0;
|
||||
while (!stop && --niters);
|
||||
return niters;
|
||||
}
|
||||
int main (void)
|
||||
{
|
||||
int i;
|
||||
struct itimerval it = { .it_interval = { .tv_sec = 0, .tv_usec = 1 },
|
||||
.it_value = { .tv_sec = 0, .tv_usec = 1 } };
|
||||
sigset_t set;
|
||||
unsigned long v[HIST];
|
||||
double tmp = 0.0;
|
||||
unsigned long n;
|
||||
signal (SIGALRM, &sighandler);
|
||||
setitimer (ITIMER_REAL, &it, NULL);
|
||||
static void sighandler (int signr)
|
||||
{
|
||||
(void) signr;
|
||||
stop = 1;
|
||||
}
|
||||
static unsigned long hog (unsigned long niters)
|
||||
{
|
||||
stop = 0;
|
||||
while (!stop && --niters);
|
||||
return niters;
|
||||
}
|
||||
int main (void)
|
||||
{
|
||||
int i;
|
||||
struct itimerval it = { .it_interval = { .tv_sec = 0, .tv_usec = 1 },
|
||||
.it_value = { .tv_sec = 0, .tv_usec = 1 } };
|
||||
sigset_t set;
|
||||
unsigned long v[HIST];
|
||||
double tmp = 0.0;
|
||||
unsigned long n;
|
||||
signal (SIGALRM, &sighandler);
|
||||
setitimer (ITIMER_REAL, &it, NULL);
|
||||
|
||||
hog (ULONG_MAX);
|
||||
for (i = 0; i < HIST; ++i) v[i] = ULONG_MAX - hog (ULONG_MAX);
|
||||
for (i = 0; i < HIST; ++i) tmp += v[i];
|
||||
tmp /= HIST;
|
||||
n = tmp - (tmp / 3.0);
|
||||
hog (ULONG_MAX);
|
||||
for (i = 0; i < HIST; ++i) v[i] = ULONG_MAX - hog (ULONG_MAX);
|
||||
for (i = 0; i < HIST; ++i) tmp += v[i];
|
||||
tmp /= HIST;
|
||||
n = tmp - (tmp / 3.0);
|
||||
|
||||
sigemptyset (&set);
|
||||
sigaddset (&set, SIGALRM);
|
||||
sigemptyset (&set);
|
||||
sigaddset (&set, SIGALRM);
|
||||
|
||||
for (;;) {
|
||||
hog (n);
|
||||
sigwait (&set, &i);
|
||||
}
|
||||
return 0;
|
||||
}
|
||||
for (;;) {
|
||||
hog (n);
|
||||
sigwait (&set, &i);
|
||||
}
|
||||
return 0;
|
||||
}
|
||||
|
||||
|
||||
References
|
||||
----------
|
||||
|
||||
http://lkml.org/lkml/2007/2/12/6
|
||||
Documentation/filesystems/proc.txt (1.8)
|
||||
- http://lkml.org/lkml/2007/2/12/6
|
||||
- Documentation/filesystems/proc.txt (1.8)
|
||||
|
||||
|
||||
Thanks
|
||||
|
|
|
|||
Loading…
Reference in a new issue