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Re: PATCH/RFC: Bring lin-lwp performance back to the real world
- From: Andrew Cagney <ac131313 at redhat dot com>
- To: Daniel Jacobowitz <drow at mvista dot com>
- Cc: gdb-patches at sources dot redhat dot com
- Date: Thu, 21 Nov 2002 23:51:01 -0500
- Subject: Re: PATCH/RFC: Bring lin-lwp performance back to the real world
- References: <20021122041123.GA21389@nevyn.them.org>
- 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