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Re: breakpoint assistance (uprobes)
- From: Roland McGrath <roland at redhat dot com>
- To: Jim Keniston <jkenisto at us dot ibm dot com>
- Cc: systemtap at sources dot redhat dot com
- Date: Tue, 20 Mar 2007 00:43:06 -0700 (PDT)
- Subject: Re: breakpoint assistance (uprobes)
> Uprobes folks have talked a fair amount amongst ourselves about
> single-stepping in multithreaded apps. This approach was on our list,
> but we haven't tried it because (1) it didn't seem very promising
> performance-wise,
I agree, but reiterate that it's never been tried in the in-kernel utrace
context to see what the performance overhead is. It certainly doesn't
scale well in the number of threads.
> and (2) it could really drive up the number of
> SIGSTOPs utrace injects into the probed process.
SIGSTOP per se is never involved.
> > Fancy VM tricks. [...]
>
> This is not currently on our radar, at least as far as code probepoints
> are concerned.
Like I said, it's a long-term prospect in my mind.
Thanks,
Roland