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

Andrew Cagney
2002-11-22T04:51:09Z

> - 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