05a5f51ca5
Replace the lkml.org links with lore to better use a single source
that's more likely to stay available long-term.
Done by bash script:
cvt_lkml_to_lore ()
{
tmpfile=$(mktemp ./.cvt_links.XXXXXXX)
header=$(echo $1 | sed 's@/lkml/@/lkml/headers/@')
wget -qO - $header > $tmpfile
if [[ $? == 0 ]] ; then
link=$(grep -i '^Message-Id:' $tmpfile | head -1 | \
sed -r -e 's/^\s*Message-Id:\s*<\s*//' -e 's/\s*>\s*$//' -e 's@^@https://lore.kernel.org/r/@')
# echo "testlink: $link"
if [ -n "$link" ] ; then
wget -qO - $link > /dev/null
if [[ $? == 0 ]] ; then
echo $link
fi
fi
fi
rm -f $tmpfile
}
git grep -P -o "\bhttps?://(?:www.)?lkml.org/lkml[\/\w]+" $@ |
while read line ; do
echo $line
file=$(echo $line | cut -f1 -d':')
link=$(echo $line | cut -f2- -d':')
newlink=$(cvt_lkml_to_lore $link)
if [[ -n "$newlink" ]] ; then
sed -i -e "s#\b$link\b#$newlink#" $file
fi
done
Link: https://lore.kernel.org/patchwork/patch/1265849/#1462688
Signed-off-by: Joe Perches <joe@perches.com>
Link: https://lore.kernel.org/r/77cdb7f32cfb087955bfc3600b86c40bed5d4104.camel@perches.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
106 lines
2.7 KiB
ReStructuredText
106 lines
2.7 KiB
ReStructuredText
========
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CPU 负载
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========
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Linux通过``/proc/stat``和``/proc/uptime``导出各种信息，用户空间工具
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如top(1)使用这些信息计算系统花费在某个特定状态的平均时间。
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例如：
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$ iostat
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Linux 2.6.18.3-exp (linmac) 02/20/2007
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avg-cpu: %user %nice %system %iowait %steal %idle
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10.01 0.00 2.92 5.44 0.00 81.63
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...
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这里系统认为在默认采样周期內有10.01%的时间工作在用户空间，2.92%的时
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间用在系统空间，总体上有81.63%的时间是空闲的。
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大多数情况下``/proc/stat``的信息几乎真实反映了系统信息，然而，由于内
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核采集这些数据的方式/时间的特点，有时这些信息根本不可靠。
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那么这些信息是如何被搜集的呢？每当时间中断触发时，内核查看此刻运行的
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进程类型，并增加与此类型/状态进程对应的计数器的值。这种方法的问题是
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在两次时间中断之间系统（进程）能够在多种状态之间切换多次，而计数器只
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增加最后一种状态下的计数。
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举例
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---
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假设系统有一个进程以如下方式周期性地占用cpu::
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两个时钟中断之间的时间线
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|-----------------------|
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^ ^
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|_ 开始运行 |
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|_ 开始睡眠
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（很快会被唤醒）
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在上面的情况下，根据``/proc/stat``的信息（由于当系统处于空闲状态时，
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时间中断经常会发生）系统的负载将会是0
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大家能够想象内核的这种行为会发生在许多情况下，这将导致``/proc/stat``
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中存在相当古怪的信息::
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/* gcc -o hog smallhog.c */
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#include <time.h>
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#include <limits.h>
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#include <signal.h>
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#include <sys/time.h>
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#define HIST 10
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static volatile sig_atomic_t stop;
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static void sighandler (int signr)
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{
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(void) signr;
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stop = 1;
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}
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static unsigned long hog (unsigned long niters)
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{
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stop = 0;
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while (!stop && --niters);
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return niters;
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}
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int main (void)
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{
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int i;
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struct itimerval it = { .it_interval = { .tv_sec = 0, .tv_usec = 1 },
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.it_value = { .tv_sec = 0, .tv_usec = 1 } };
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sigset_t set;
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unsigned long v[HIST];
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double tmp = 0.0;
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unsigned long n;
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signal (SIGALRM, &sighandler);
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setitimer (ITIMER_REAL, &it, NULL);
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hog (ULONG_MAX);
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for (i = 0; i < HIST; ++i) v[i] = ULONG_MAX - hog (ULONG_MAX);
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for (i = 0; i < HIST; ++i) tmp += v[i];
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tmp /= HIST;
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n = tmp - (tmp / 3.0);
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sigemptyset (&set);
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sigaddset (&set, SIGALRM);
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for (;;) {
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hog (n);
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sigwait (&set, &i);
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}
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return 0;
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}
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参考
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---
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- https://lore.kernel.org/r/loom.20070212T063225-663@post.gmane.org
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- Documentation/filesystems/proc.rst (1.8)
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谢谢
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---
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Con Kolivas, Pavel Machek
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