Re: kern/45734: performance regression for sequential/random creation of files, as well as stat(2) (ffs fs)

[jean-Yves Migeon <jym%NetBSD.org@localhost>]

The following reply was made to PR kern/45734; it has been noted by GNATS.

From: jean-Yves Migeon <jym%NetBSD.org@localhost>
To: <gnats-bugs%NetBSD.org@localhost>
Cc: <kern-bug-people%netbsd.org@localhost>, <gnats-admin%netbsd.org@localhost>,
 <netbsd-bugs%netbsd.org@localhost>
Subject: Re: kern/45734: performance regression for sequential/random  creation 
of files, as well as stat(2) (ffs fs)
Date: Fri, 23 Dec 2011 11:50:18 +0100

 On Fri, 23 Dec 2011 05:30:07 +0000 (UTC), David Holland wrote:
 >  On Thu, Dec 22, 2011 at 11:30:00PM +0000, jym%NetBSD.org@localhost wrote:
 >   > I narrowed the regression to this window:
 >   >
 >   > GENERIC 2011-07-03
 >   > seq_create ran_create ran_stat (#/s)
 >   > 4374 4499 6052
 >   > 4488 4553 6008
 >   > 4616 4574 6057
 >   > GENERIC 2011-07-05
 >   > seq_create ran_create ran_stat (#/s)
 >   > 1518 1539 1698
 >   > 1534 1521 1689
 >   > 1532 1541 1713
 >
 >  On July 3 DIAGNOSTIC was turned on by default. Can you (1) check if
 >  that's really one of the differences between your two endpoints, and
 >  (2) if so turn it off in the July 5 kernel and see what the
 >  performance looks like?
 >
 >  DIAGNOSTIC is not supposed to be expensive but that isn't 
 > necessarily
 >  working right.
 >
 >  The only fs-related commits I see in the period are manu@'s extattr
 >  cleanup, and that isn't really very credible as a source of
 >  performance problems.
 > [snip]
 >  Log Message:
 >  - fix a use-after-free bug in uvm_km_free.
 >    (after uvm_km_pgremove frees pages, the following pmap_remove
 > touches them.)
 >  - acquire the object lock for operations on pmap_kernel as it can
 > actually be
 >    raced with P->V operations.  eg. pagedaemon.
 
 Came to the same conclusion this morning. Will check.
 
 Merry christmas to all!
 
 -- 
 Jean-Yves Migeon
 jym%NetBSD.org@localhost