From: Matthew Wilcox <willy@debian.org>
To: "Van Maren, Kevin" <kevin.vanmaren@unisys.com>
Cc: "'Matthew Wilcox '" <willy@debian.org>,
"''Linus Torvalds ' '" <torvalds@transmeta.com>,
"''Jeremy Fitzhardinge ' '" <jeremy@goop.org>,
"''William Lee Irwin III ' '" <wli@holomorphy.com>,
"''linux-ia64@linuxia64.org ' '" <linux-ia64@linuxia64.org>,
"''Linux Kernel List ' '" <linux-kernel@vger.kernel.org>,
"''rusty@rustcorp.com.au ' '" <rusty@rustcorp.com.au>,
"''dhowells@redhat.com ' '" <dhowells@redhat.com>,
"''mingo@elte.hu ' '" <mingo@elte.hu>
Subject: Re: [Linux-ia64] reader-writer livelock problem
Date: Fri, 8 Nov 2002 19:19:07 +0000 [thread overview]
Message-ID: <20021108191907.N12011@parcelfarce.linux.theplanet.co.uk> (raw)
In-Reply-To: <3FAD1088D4556046AEC48D80B47B478C0101F4EE@usslc-exch-4.slc.unisys.com>; from kevin.vanmaren@unisys.com on Fri, Nov 08, 2002 at 12:05:30PM -0600
On Fri, Nov 08, 2002 at 12:05:30PM -0600, Van Maren, Kevin wrote:
> Absolutely you should minimize the locking contention.
> However, that isn't always possible, such as when you
> have 64 processors contending on the same resource.
if you've got 64 processors contending on the same resource, maybe you
need to split that resource up so they can have a copy each. all that
cacheline bouncing can't do your numa boxes any good.
> With the current kernel, the trivial example with reader/
> writer locks was having them all call gettimeofday().
i hear x86-64 has a lockless gettimeofday. maybe that's the solution.
> But try having 64 processors fstat() the same file,
> which I have also seen happen (application looping,
> waiting for another process to finish setting up the
> file so they can all mmap it).
umm.. the call trace:
sys_fstat
|-> vfs_fstat
| |-> fget
| |-> read_lock(&files->file_lock)
| |-> vfs_getattr
| |-> inode->i_op->getattr
| |-> generic_fillattr
|-> cp_new_stat64
|-> memset
|-> copy_to_user
so you're talking about contention on files->file_lock, right? it's really
not the kernel's fault that your app is badly written. that lock's private
to process & children, so it's not like another application can hurt you.
> What MCS locks do is they reduce the number of times
> the cacheline has to be flung around the system in
> order to get work done: they "scale" much better with
> the number of processors: O(N) instead of O(N^2).
yes, but how slow are they in the uncontended case?
--
Revolutions do not require corporate support.
next prev parent reply other threads:[~2002-11-08 19:12 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-11-08 18:05 [Linux-ia64] reader-writer livelock problem Van Maren, Kevin
2002-11-08 19:19 ` Matthew Wilcox [this message]
2002-11-08 19:26 ` David Mosberger
-- strict thread matches above, loose matches on Subject: below --
2002-11-08 20:24 Van Maren, Kevin
2002-11-08 20:17 Van Maren, Kevin
2002-11-08 20:39 ` Matthew Wilcox
2002-11-08 17:41 Van Maren, Kevin
2002-11-08 17:52 ` Matthew Wilcox
[not found] <3FAD1088D4556046AEC48D80B47B478C0101F4E7@usslc-exch-4.slc.unisys.com>
2002-11-08 3:51 ` William Lee Irwin III
2002-11-08 17:13 ` Jeremy Fitzhardinge
2002-11-08 17:25 ` Linus Torvalds
2002-11-08 17:28 ` Linus Torvalds
2002-11-08 17:38 ` Jeremy Fitzhardinge
2002-11-08 17:43 ` David Howells
2002-11-08 17:57 ` Linus Torvalds
2002-11-09 2:48 ` Rusty Russell
2002-11-09 4:36 ` William Lee Irwin III
2002-11-08 17:34 ` David Howells
2002-11-08 17:54 ` David Howells
2002-11-08 17:55 ` Stephen Hemminger
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