Re: Testing 7.0 Beta: FFS still very slow when creating files

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

   Date: Fri, 22 Aug 2014 17:59:37 +0200
   From: Stephan <stephanwib%googlemail.com@localhost>

   Has anybody an idea on this or how to track this down? At the moment,
   I can't even enter ddb using Strg+Alt+Esc keys for some reason. I've
   also seen people playing with dtrace but that doesn't seem to be
   included.

Dtrace may be a good idea.  You can use it by

(a) using a kernel built with `options KDTRACE_HOOKS',
(b) using a userland built with MKDTRACE=yes,
(c) modload /stand/ARCH/VERSION/solaris.kmod
    modload /stand/ARCH/VERSION/dtrace.kmod
    modload /stand/ARCH/VERSION/fbt.kmod
    modload /stand/ARCH/VERSION/sdt.kmod
(d) mkdir /dev/dtrace && mknod /dev/dtrace/dtrace c dtrace

(Yes, this is too much work.  Someone^TM should turn it all on by
default for netbsd-7...!)

From the lockstat output it looks like there's a lot of use of
mntvnode_lock, which suggests this may be related to hannken@'s vnode
cache changes.  Might be worthwhile to sample stack traces of
vfs_insmntque, with something like

dtrace -n 'fbt::vfs_insmntqueue:entry { @[stack()]++ }'

or perhaps sample stack traces of the mutex_enters of mntvnode_lock.