问题描述
iostat -x -d
可以显示许多I/O统计信息.对于iostat的实用程序，解释为:
can display many i/o statistic info. For util of iostat, the explanation is :
我想知道util是如何计算的?
I want to know how the util was computed?
我做一个实验，(请参见以下代码)，启动40个线程以随机读取40个文件.我认为磁盘使用率应该很高，但是我错了，iostat如下，任何人都可以给出原因? THX
I make an experiment, (see following code), start 40 thread to randomly read 40 files. I suppose the disk util should be very high, but I am wrong, the iostat is as follow, anyone can give why? THX
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sdb1 0.01 0.44 0.24 0.57 3.44 8.14 14.34 0.00 2.28 0.66 0.05
代码:
#include <iostream>
#include <fstream>
#include <pthread.h>
using namespace std;
void* work(void* a)
{
int* id = (int*)a;
string file = "sys.partition";
char buf[100];
sprintf(buf, "%d", *id);
file.append(string(buf));
ifstream in(file.c_str());
in.seekg(0, ios_base::end);
size_t len = in.tellg();
cout << "open file : " << file << " , " << len << endl;
srand(time(NULL));
while(true)
{
size_t pos = rand() % len;
in.seekg(pos);
//cout << pos << endl;
in.read(buf, 10);
system("sync");
}
in.close();
}
int main(int argc, char** argv)
{
static const int num = 40;
pthread_t threads[num];
for (int i = 0; i < num; i++) {
pthread_create(&threads[i], NULL, work, &i);
}
for (int i = 0; i < num; i++) {
pthread_join(threads[i], NULL);
}
return 0;
}
在iostat的源代码中，
推荐答案
%util被命名为busy: https://code.google.com/p/tester-higkoo/source/browse/trunk/Tools/iostat/iostat .c#380
%util is named busy in the source code of iostat: https://code.google.com/p/tester-higkoo/source/browse/trunk/Tools/iostat/iostat.c#380
忙碌被计算为Ticks与deltams的百分比，限制为100％
Busy is counted as percent ratio of Ticks to deltams, limited to 100%
busy = 100.0 * blkio.ticks / deltams; /* percentage! */
if (busy > 100.0) busy = 100.0;
DeltaMS是一段时间(用户时间+系统时间+空闲时间+ iowait)/ncpu中系统负载的总和.
DeltaMS is sum of system load for the period of time (user time + system time + idle time + iowait)/ ncpu.
double deltams = 1000.0 *
((new_cpu.user + new_cpu.system +
new_cpu.idle + new_cpu.iowait) -
(old_cpu.user + old_cpu.system +
old_cpu.idle + old_cpu.iowait)) / ncpu / HZ;
Ticks-是期间的Time of requests in queue
Ticks - is the Time of requests in queue for the period
blkio.ticks = new_blkio[p].ticks
- old_blkio[p].ticks;
在最新版本的sysstat中，代码有点不同: http://sources.debian.net/src/sysstat /10.2.0-1/iostat.c#L959
In more current version of sysstat the code is bit different: http://sources.debian.net/src/sysstat/10.2.0-1/iostat.c#L959
/* rrq/s wrq/s r/s w/s rsec wsec rqsz qusz await r_await w_await svctm %util */
printf(" %8.2f %8.2f %7.2f %7.2f %8.2f %8.2f %8.2f %8.2f %7.2f %7.2f %7.2f %6.2f %6.2f\n",
...
/*
* Again: Ticks in milliseconds.
* In the case of a device group (option -g), shi->used is the number of
* devices in the group. Else shi->used equals 1.
*/
shi->used ? xds.util / 10.0 / (double) shi->used
: xds.util / 10.0); /* shi->used should never be null here */
xds填充在compute_ext_disk_stats(&sdc, &sdp, itv, &xds); http://sources.debian.net/src/sysstat/10.2.0-1/common.c?hl=679#L679
/*
* Macros used to display statistics values.
*
* HZ is 1024 on IA64 and % should be normalized to 100.
*/
#define S_VALUE(m,n,p) (((double) ((n) - (m))) / (p) * HZ)
xds->util = S_VALUE(sdp->tot_ticks, sdc->tot_ticks, itv);
还有来自iostat.c的tot_ticks的填充
And there is the filling of tot_ticks from iostat.c
* @ioi Current sample statistics.
* @ioj Previous sample statistics.
* @itv Interval of time.
...
sdc.tot_ticks = ioi->tot_ticks;
sdp.tot_ticks = ioj->tot_ticks;
从read_sysfs_file_stat( iostat.c:487 )，而ioi和ioj是当前状态和以前的状态.
tot_ticks are read from "sysfs stat for current block device or partition" in read_sysfs_file_stat (iostat.c:487), and ioi and ioj are current and previous stat.
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