Re: [9fans] "Blocks" in C

[drivers@0xabadba.be]

     Is there some method of lock profiling on plan9?  For example when I do work on freebsd and say remove a giant lock from the keyboard subsystem; I run the lock profiler before and after the change to see how long the system was sitting at the in kernel locks.  
     I am doing my thesis (undergrad) on these kind of topics and am interested in seeing how I may be of use.

=jt
------Original Message------
From: erik quanstrom
Sender: 9fans-bounces@9fans.net
To: 9fans@9fans.net
ReplyTo: Fans of the OS Plan 9 from Bell Labs
Subject: Re: [9fans] "Blocks" in C
Sent: Sep 18, 2009 07:41

> it isn't really a `big kernel lock' in the linux sense.

you're right, technically it is a very different problem.

the effects seem similar.  the lock is just in the block allocator
rather than the syscall interface.  if you're doing a lot of i/o
in a standard kernel, there's a lot of block allocation.

> with error checking. an alternative allocator that uses quickfit on top of
> a variant of the simple allocator in kernighan and ritchie is
> roughly 30 times faster on some malloc-thrashing tests (i'm just remembering that
> from tests i did last year, so i might have the number wrong, but it's substantial).

i see the same thing.  with the allocator in a specific packet-pushing
test, i see 185000 packets/s, with a block pool i see ~450000 packets/s.
all the packets are the same size.

would you be willing to share your allocator?  this may help a number
of cases i'm currently fighting.  10gbe and 2×10gbe + quad processors
have a way of putting a sharp point on an otherwise dull problem.

i also wonder if an ilock is really the right protection
mechanism on machines with 8 or 16 logical processors
for malloc.

the reason i mention this is that it turns out that the lock
on block pools can be hot enough that splitting the lock
per controller can have a big positive effect.  i need to set
up a faster target, but i've seen significant jumps in bandwidth
for 2 82563 controllers when using 2 pools instead of one
even on a fairly bored machine.

sorry for the lack of real numbers.

- erik



=jt