Re: [PATCH v2 0/8] Demangle minimal symbol names in worker threads

[Tom Tromey <tom@tromey.com>]

Tom> Locally I only saw utilization of 1.5 CPUs or so -- so, not very
Tom> parallel yet.

I found the "mutrace" tool and it looks like the new mutex is heavily
contended.  This is pretty much what I suspected, but still unfortunate.

$ mutrace -d ./gdb -nx -batch ./gdb
[...]
 Mutex #   Locked  Changed    Cont. tot.Time[ms] avg.Time[ms] max.Time[ms]  Flags
       2  3714780    45723    26425      975.514        0.000       22.141 M-.--.

I'm not really sure what to do about it.

I do wonder if there are many duplicates when demangling minsym names.
One idea would be to demangle in parallel and only then fill in the
table.

A similar problem will occur when/if we want to parallelize psymbol
reading.  Those use the demangle hash table, but also the bcache.  (The
bcache is important, but I found recently that the demangling isn't
really needed -- the names are demangled due to the physname work, and
the demangle hash table is only used to ensure that the bcache gives
good results.  Removing the demangling step here can also provide a nice
speedup...)

Tom