Re: Busy-wait delay in qmail 1.03 after upgrading to Linux 2.6

[Andrew Morton]

Haakon Riiser <hakonrk@xxxxxxxxxxxx> wrote:
>
> > Output from time:
> > 
> >   real    0m0.309s
> >   user    0m0.011s
> >   sys     0m0.004s
> 
> Just wanted to comment on my own data, since I just noticed it myself:
> 
> The output from time indicates that the system is _not_ using CPU
> while delaying, so you might wonder why I said it did.  The reason
> is that I'm using an AfterStep applet (ascpu) to monitor CPU usage,
> and it appeared to work fine in 2.6.  Now, I see that there are
> differences:  For example, another problem I encountered while
> upgrading to 2.6 was that disk intensive jobs, such as updating
> the slocate database, made ascpu report 100% CPU usage.  I just
> ran top (procps 2.0.16) beside it, and it reported approximately
> 10% CPU usage, which is no more than 2.4 used.

2.6 has finer-grained cpu utilisation accounting; probably ascpu is
accidentally lumping I/O wait into system time.

Still, some of those delays seem excessive and if you indeed are seeing
longer runtimes than with 2.4, something is up.

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