Top not showing cpu usage even remotely accurately

[Tamouh H.]

> 
> In recent 6.X versions, you can use 'S' to show system threads too.
> For an even more fine-grained view, you can use 'H' to show 
> each thread separately.
> 
> Then there is also the 'CPU' mode (as opposed to the default 'WCPU'
> mode of top).
> 
> > I've the same issue with FBSD 5.4 and TOP. In fact, the 
> load averages 
> > are so irrelevant now that I barely pay attention to them. 
> The server 
> > goes to 4 or 6 load averages without slowing down, and 
> other times the 
> > load average would be 0.8 and the server is running slow.
> 
> Probably because the work it does at the moment is not CPU-bounded?
> 
> > An example of unmatching TOP:
> > 
> > last pid: 17889;  load averages:  0.60,  0.52,  0.50        
>                                           up 3+17:22:33  00:41:45
> > 186 processes: 2 running, 183 sleeping, 1 lock CPU states: 
> 30.0% user,  
> > 0.0% nice,  1.7% system,  0.1% interrupt, 68.3% idle
> > Mem: 1678M Active, 1110M Inact, 287M Wired, 87M Cache, 112M 
> Buf, 103M 
> > Free
> > Swap: 8762M Total, 1584K Used, 8760M Free
> > 
> >   PID USERNAME PRI NICE   SIZE    RES STATE  C   TIME   
> WCPU    CPU COMMAND
> >  5071 nobody   101    0 43124K 35180K CPU2   2   0:07 
> 14.89% 14.89% httpd
> > 14409 nobody     4    0 43940K 36076K sbwait 0   0:01  
> 1.22%  1.22% httpd
> > 95515 nobody     4    0 39892K 32188K sbwait 1   0:08  
> 0.29%  0.29% httpd
> 
> Try hitting 'S'.  Perhaps the system spends too much time in 
> system threads (i.e. the "syncer") :)
> 

I think TOP and load averages are no longer accurate on FBSD 5.x and 6.x with SMP kernel. As far as I've seen. Load averages hit sometimes 8.0 without a noticable degradation in performance.

This is one TOP that freaked me out, notice Idle CPU is 70% while the process is showing it is using 99% of CPU. systat draws more accurate picture, however, load average is still useless as far as performance monitoring :

last pid: 10174;  load averages:  1.63,  1.44,  1.20                                                  up 4+00:25:19  00:39:20
169 processes: 2 running, 166 sleeping, 1 zombie
CPU states: 25.8% user,  0.0% nice,  0.7% system,  0.1% interrupt, 73.4% idle
Mem: 1316M Active, 1445M Inact, 297M Wired, 127M Cache, 112M Buf, 79M Free
Swap: 8762M Total, 2096K Used, 8760M Free

  PID USERNAME PRI NICE   SIZE    RES STATE  C   TIME   WCPU    CPU COMMAND
13362 root     111    0 36444K 34196K CPU3   3  50:06 98.88% 98.88% perl5.8.7
90391 root      96    0 27356K 26236K select 2   0:06  0.54%  0.54% perl5.8.7
79619 nobody     4    0   209M 84640K sbwait 1   0:09  0.39%  0.39% httpd
10161 root      97    0  6712K  4752K select 2   0:00  1.40%  0.20% exim-4.62-0
79649 nobody    20    0   210M 84464K lockf  0   0:06  0.15%  0.15% httpd
10158 mailnull   4    0  6760K  3992K sbwait 2   0:00  0.81%  0.15% exim-4.62-0
79654 nobody     4    0   208M 68660K sbwait 0   0:08  0.05%  0.05% httpd
79660 nobody     4    0   208M 58144K sbwait 0   0:06  0.05%  0.05% httpd
10170 sshd     117    0  4768K  2052K select 0   0:00  1.00%  0.05% sshd
 1123 mysql     96    0   346M   214M select 2 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 3 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 3 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 2 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 0 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 2 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 1 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 0 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 0 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 3 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 3 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 0 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 1 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 2 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 1 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 1 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 0 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 0 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 2 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 1 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 0 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 2 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 0 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 1 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 0 114:48  0.00%  0.00% mysqld
 1123 mysql     20    0   346M   214M kserel 1 114:48  0.00%  0.00% mysqld