Re: PATCH/RFC: Bring lin-lwp performance back to the real world

[Andrew Cagney <ac131313@redhat.com>]

>  - It's such a wonderful bandaid that a lot of the badly needed
>    cleanups may lose momentum.

``Don't you worry about that'' :-)

A back of envelope calculation shows:

> Plucking a ``random'' memory location out of thin air:
> 
> cagney@torrens$ grep 0x40040ea0 gdb.strace | grep ptrace | wc -l
>    7038

For <160 stops, GDB fetched a thread-db buffer 7000 times.  So, GDB is 
fetching an identical buffer 7000/160 ~= 50 times for every stop!

> cagney@torrens$ expr 7038 \* 250
> 1759500

250?  I happen to know that the buffer is ~1000 bytes long which gives 
us 250 (1000/sizeof(long) ptrace() calls for every buffer transfer.

The patch addresses the second problem, but not the first.  While it 
releaves a bit of steam, there is still plenty of oportunity to further 
ramp up the performance by several more orders of magnitude.

(BTW, this sort of brain-deadness on the part of GDB explains why other 
minor performance tweeks had zero benefit :-)

----

Note that the other /proc trickery is in linux-proc.c.  Should this be 
there?

Andrew