转载：http://blog.chinaunix.net/uid-20057401-id-1979033.html
前几天要写一个取得linux performance的函数。查询了一些资料。发现有几种计算cpu利用率的方法。但是都不怎么正确。最后查了以下top的源代码。现列出其计算cpu利用率的关键函数
c代码如下：
typedef struct CPU_t {
TIC_t u, n, s, i, w, x, y, z; // as represented in /proc/stat
TIC_t u_sav, s_sav, n_sav, i_sav, w_sav, x_sav, y_sav, z_sav; // in the order of our display
unsigned id; // the CPU ID number
} CPU_t;
c代码实现如下：
static CPU_t *cpus_refresh (CPU_t *cpus)
{
static FILE *fp = NULL;
int i;
int num;
// enough for a /proc/stat CPU line (not the intr line)
char buf[SMLBUFSIZ];
/* by opening this file once, we'll avoid the hit on minor page faults
(sorry Linux, but you'll have to close it for us) */
if (!fp) {
if (!(fp = fopen("/proc/stat", "r")))
std_err(fmtmk("Failed /proc/stat open: %s", strerror(errno)));
/* note: we allocate one more CPU_t than Cpu_tot so that the last slot
can hold tics representing the /proc/stat cpu summary (the first
line read) -- that slot supports our View_CPUSUM toggle */
cpus = alloc_c((1 + Cpu_tot) * sizeof(CPU_t));
}
rewind(fp);
fflush(fp);
// first value the last slot with the cpu summary line
if (!fgets(buf, sizeof(buf), fp)) std_err("failed /proc/stat read");
cpus[Cpu_tot].x = 0; // FIXME: can't tell by kernel version number
cpus[Cpu_tot].y = 0; // FIXME: can't tell by kernel version number
cpus[Cpu_tot].z = 0; // FIXME: can't tell by kernel version number
num = sscanf(buf, "cpu %Lu %Lu %Lu %Lu %Lu %Lu %Lu %Lu",
&cpus[Cpu_tot].u,
&cpus[Cpu_tot].n,
&cpus[Cpu_tot].s,
&cpus[Cpu_tot].i,
&cpus[Cpu_tot].w,
&cpus[Cpu_tot].x,
&cpus[Cpu_tot].y,
&cpus[Cpu_tot].z
);
if (num < 4)
std_err("failed /proc/stat read");
// and just in case we're 2.2.xx compiled without SMP support...
if (Cpu_tot == 1) {
cpus[1].id = 0;
memcpy(cpus, &cpus[1], sizeof(CPU_t));
}
// now value each separate cpu's tics
for (i = 0; 1 < Cpu_tot && i < Cpu_tot; i++) {
if (!fgets(buf, sizeof(buf), fp)) std_err("failed /proc/stat read");
cpus[i].x = 0; // FIXME: can't tell by kernel version number
cpus[i].y = 0; // FIXME: can't tell by kernel version number
cpus[i].z = 0; // FIXME: can't tell by kernel version number
num = sscanf(buf, "cpu%u %Lu %Lu %Lu %Lu %Lu %Lu %Lu %Lu",
&cpus[i].id,
&cpus[i].u, &cpus[i].n, &cpus[i].s, &cpus[i].i, &cpus[i].w, &cpus[i].x, &cpus[i].y, &cpus[i].z
);
if (num < 4)
std_err("failed /proc/stat read");
}
return cpus;
}
c 代码实现如下：
static void summaryhlp (CPU_t *cpu, const char *pfx)
{
// we'll trim to zero if we get negative time ticks,
// which has happened with some SMP kernels (pre-2.4?)
#define TRIMz(x) ((tz = (SIC_t)(x)) < 0 ? 0 : tz)
SIC_t u_frme, s_frme, n_frme, i_frme, w_frme, x_frme, y_frme, z_frme, tot_frme, tz;
float scale;
u_frme = cpu->u - cpu->u_sav;
s_frme = cpu->s - cpu->s_sav;
n_frme = cpu->n - cpu->n_sav;
i_frme = TRIMz(cpu->i - cpu->i_sav);
w_frme = cpu->w - cpu->w_sav;
x_frme = cpu->x - cpu->x_sav;
y_frme = cpu->y - cpu->y_sav;
z_frme = cpu->z - cpu->z_sav;
tot_frme = u_frme + s_frme + n_frme + i_frme + w_frme + x_frme + y_frme + z_frme;
if (tot_frme < 1) tot_frme = 1;
scale = 100.0 / (float)tot_frme;
// display some kinda' cpu state percentages
// (who or what is explained by the passed prefix)
show_special(
0,
fmtmk(
States_fmts,
pfx,
(float)u_frme * scale,
(float)s_frme * scale,
(float)n_frme * scale,
(float)i_frme * scale,
(float)w_frme * scale,
(float)x_frme * scale,
(float)y_frme * scale,
(float)z_frme * scale
)
);
Msg_row += 1;
// remember for next time around
cpu->u_sav = cpu->u;
cpu->s_sav = cpu->s;
cpu->n_sav = cpu->n;
cpu->i_sav = cpu->i;
cpu->w_sav = cpu->w;
cpu->x_sav = cpu->x;
cpu->y_sav = cpu->y;
cpu->z_sav = cpu->z;
#undef TRIMz
}
