Re: Two observations using GDB 13 snapshot

[Eli Zaretskii <eliz@gnu.org>]

> From: Tom Tromey <tom@tromey.com>
> Cc: Tom Tromey <tom@tromey.com>,  gdb-patches@sourceware.org,
>   luis.machado@arm.com
> Date: Sat, 24 Dec 2022 10:57:53 -0700
> 
> Eli> So you are saying that the rewrite of the DWARF scanner could be the
> Eli> reason for the slowness?
> 
> No, sorry.
> 
> -readnow should not be affected much, if at all, by the rewrite.  The
> new code is not used when -readnow is given.  There's a case in
> dwarf2_initialize_objfile that ensures this.
> 
> -readnow is just generally much slower because it does a lot more work.
> I don't know why it would have slowed down between 12 and 13, though.
> 
> Eli> Let me know if I can provide any additional information that could be
> Eli> useful in investigating this.
> 
> Eli> Would it be useful to open a bugzilla issue?
> 
> The best thing would be some kind of comparison of profiles between the
> two versions, to try to see what caused the slowdown.  However, that's a
> lot of work.
> 
> FWIW I tend not to pay much attention to -readnow.  I never use it
> myself and I try to dissuade others from using it as well.

 -readnow doesn't interest me (I never use it), except as some evidence
 or data point regarding the slow reading of debug info.

All I'm interested in is to help you and others understand what could
be the reason for slow reading of debug info at startup, so that it
could be sped up at some point.