From: Al Viro <viro@ZenIV.linux.org.uk>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Waiman Long <Waiman.Long@hp.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
"Chandramouleeswaran, Aswin" <aswin@hp.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: spinlock contention of files->file_lock
Date: Tue, 1 Oct 2013 02:53:44 +0100 [thread overview]
Message-ID: <20131001015344.GV13318@ZenIV.linux.org.uk> (raw)
In-Reply-To: <1380589503.5326.13.camel@edumazet-glaptop.roam.corp.google.com>
On Mon, Sep 30, 2013 at 06:05:03PM -0700, Eric Dumazet wrote:
> Speaking of spinlock contention, the files->file_lock is a good example.
>
> Multi threaded programs hit this spinlock three times per fd :
>
> alloc_fd() / fd_install() / close()
>
> I think fd_install() could be done without this spinlock.
The problem is dup2(), not table resize... I'm not saying it can't be
done, but it won't be trivial and you seem to be looking for potential
trouble in the wrong place. dup2() semantics is the real bitch.
What we want is
* dup2() over unused descriptor => insert and be done with that
* dup2() over opened one => replace and do equivalent of close()
for what had been there before
The trouble is, what to do with dup2() over reserved, but still not
installed descriptor? We handle that as -EBUSY and we use ->file_lock
to get atomicity wrt transitions between those states.
And yes, dup2() is a lousy API in multithreaded situation. It's still
there... See comments in do_dup2() for some amusement.
next prev parent reply other threads:[~2013-10-01 1:53 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-30 19:29 Avoiding the dentry d_lock on final dput(), part deux: transactional memory Linus Torvalds
2013-09-30 20:01 ` Waiman Long
2013-09-30 20:04 ` Linus Torvalds
2013-10-02 14:56 ` Andi Kleen
2013-09-30 22:52 ` Benjamin Herrenschmidt
2013-10-01 0:36 ` Michael Neuling
2013-10-01 0:56 ` Linus Torvalds
2013-10-01 2:05 ` Benjamin Herrenschmidt
2013-10-01 3:13 ` Paul E. McKenney
2013-10-01 4:52 ` Michael Neuling
2013-10-01 12:16 ` Paul E. McKenney
2013-10-01 13:42 ` Paul E. McKenney
2013-10-01 1:05 ` spinlock contention of files->file_lock Eric Dumazet
2013-10-01 1:44 ` Linus Torvalds
2013-10-01 2:18 ` Eric Dumazet
2013-10-01 21:41 ` Eric Dumazet
2013-10-01 22:04 ` Al Viro
2013-10-01 22:21 ` Eric Dumazet
2013-10-02 5:13 ` Ingo Molnar
2013-10-02 10:20 ` Al Viro
2013-10-02 10:56 ` Ingo Molnar
2013-10-01 1:53 ` Al Viro [this message]
2013-10-01 2:02 ` Linus Torvalds
2013-10-01 3:27 ` Al Viro
2013-10-01 3:36 ` Eric Dumazet
2013-10-01 5:12 ` Eric Dumazet
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20131001015344.GV13318@ZenIV.linux.org.uk \
--to=viro@zeniv.linux.org.uk \
--cc=Waiman.Long@hp.com \
--cc=aswin@hp.com \
--cc=benh@kernel.crashing.org \
--cc=eric.dumazet@gmail.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).