D. Hugh Redelmeier wrote:
On Thu, 5 Jul 2007, Dave Anderson wrote:
| From: Dave Anderson <anderson@xxxxxxxxxx>
| D. Hugh Redelmeier wrote:
| > | From: Dave Anderson <anderson@xxxxxxxxxx>
| >
| > | D. Hugh Redelmeier wrote:
| >
| > | > ==> Worse: while it is awaiting my RETURN, it is burning 100% of the
| > | > CPU!
| Again, what exactly do you do to reproduce it? I just cannot get the 100%
| cpu-time waiting on the "less" sub-shell.
The simplest example, in a 24-line xterm:
$ su
# crash
crash> help set
(I think that he su is necessary because crash is examining the live
kernel.)
This behaviour comes up whenever crash is using more for more than a page.
Except "crash --help" which seems to be different.
Interesting, yeah, I can see it with "help set", although not necessarily
with most other help commands that use more than a page. Strange...
This machine is an Athlon X2 running an up-to-date x86_64 Fedora 7.
Mind you, only one core is enabled (because of a kernel bug that is
the motivation for using crash).
The CPU goes to 100%. I presume that most of it is in the kernel,
handling the waitpid.
Right -- it's essentially becomes an alternate idle loop for that cpu...
Harmless, but annoying.
This seems really easy for me to reproduce. What happens when you try
this? In what environment?
| Anyway, I'm going to have to be able to reproduce it and test any
| changes thoroughly before potentially re-introducing the hangs I
| used to see.
Sure. And my suggestion was not tested even by me. It was only part
of an argument showing that the current code is wrong.
If you have a version of crash waiting for the pager to finish (as in my
example), put a gdb on it to find out just where in crash it is
waiting. (I've told you where mine is waiting.)
I suspect that your crash would not be in a waitpid loop because that
would be a busy wait and you say you don't see a busy wait.
I wasn't able to reproduce the 99% cpu usage (until now).
But yes, it's in the same place in restore_sanity() that
you were seeing.
Dave
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