Re: [Valgrind-users] valgrind running REALLY slow, then no output

[Nicholas N. <nj...@ca...>]

On Wed, 30 Jul 2003, Jenny Lighthart wrote:

> I used to be able to run valgrind on my program in a reasonable time
> period - 5 to 10 times slower than the program runs without it.  Then,
> some new code was introduced into the program.  After this, valgrind
> runs excruciatingly slow and when it finishes it claims "0 errors from 0
> contexts" and "0 bytes lost in 0 blocks".  Before this new code was
> introduced, there were numerous errors reported by valgrind.
>
> What I am running is a CppUnit test that isolates the newly introduced
> code.  When not under valgrind, the test completes in 4 seconds.  When
> running under valgrind it takes 13 minutes 54 seconds.  Into this test I
> intentionally created a string variable on the heap and never deleted
> it.  The valgrind output did catch this leak, but reported no memory
> errors - which I really don't believe.
>
> Could this be because my program is doing something not supported by
> valgrind? Any ideas for figuring out where it is getting hung up?

Generally if a program does something Valgrind can't handle, Valgrind
aborts immediately.  Valgrind doesn't run some kinds of code very well;
I don't know the details much, but I think the way the scheduler handles
syscalls, particularly blocking ones, can sometimes cause programs to run
excessively slowly.  Others know more about this than I do.  If you can
give some more details about what the added code is doing, that might be
useful, although it's hard to say exactly what information would be
relevant, since I don't understand this too well.

N