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Re: gdb/457: GDB runs slow (internal doco needed) (FAQ)
- From: Andrew Cagney <ac131313 at redhat dot com>
- To: nobody at sources dot redhat dot com
- Cc: gdb-prs at sources dot redhat dot com,
- Date: 28 Nov 2002 18:58:01 -0000
- Subject: Re: gdb/457: GDB runs slow (internal doco needed) (FAQ)
- Reply-to: Andrew Cagney <ac131313 at redhat dot com>
The following reply was made to PR gdb/457; it has been noted by GNATS.
From: Andrew Cagney <ac131313@redhat.com>
To: gdb-gnats@sources.redhat.com
Cc:
Subject: Re: gdb/457: GDB runs slow (internal doco needed) (FAQ)
Date: Thu, 28 Nov 2002 13:50:19 -0500
http://sources.redhat.com/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gdb&pr=457
For an update on the thread problem, see:
http://sources.redhat.com/ml/gdb/2002-11/msg00316.html
GDB wasn't so much slow, as catatonic.
Turns out that GDB was doing several million ptrace() memory reads for
roughly 1000 single steps.
Given that, the overhead of stopping/starting threads, or fetching
registers, is seriously in the noise.
While things have been improved, more improvement is possible.
The one post mortem comment here, I think, is that (as people teaching
one how to use profile tools are quick to remind us), it isn't what you
know but what you don't know that is important. The numbers returned by
profile, for instance, were singularly misleading :-(
Andrew