From: Linus Torvalds <torvalds@linux-foundation.org>
To: Waiman Long <waiman.long@hpe.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
"Chen, Tim C" <tim.c.chen@intel.com>,
Ingo Molnar <mingo@redhat.com>, Davidlohr Bueso <dbueso@suse.de>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Jason Low <jason.low2@hp.com>,
Michel Lespinasse <walken@google.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Waiman Long <waiman.long@hp.com>,
Al Viro <viro@zeniv.linux.org.uk>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: performance delta after VFS i_mutex=>i_rwsem conversion
Date: Mon, 6 Jun 2016 14:20:32 -0700 [thread overview]
Message-ID: <CA+55aFzOCnz-pgFG8AvV5NkXo_NU6ri9XtaJhfV5RpypOEJn+w@mail.gmail.com> (raw)
In-Reply-To: <5755E782.90800@hpe.com>
On Mon, Jun 6, 2016 at 2:13 PM, Waiman Long <waiman.long@hpe.com> wrote:
>
> The tricky part about optimistic spinning in rwsem is that we don't know for
> sure if any of the lock holding readers is running or not.
I'm notm sure how common the reader-vs-writer contention is, at least
for the new inode use. I'm sure you can trigger it with crazy
benchmarks, but I wouldn't worry about it unless people start
complaining.
The writer-writer case is easy to trigger with write-heavy loads (ok,
rename/unlink in this case). Are there real loads where there are lots
of concurrent lookup and writes? I really don't know (note that
"lookup" needs to be uncached and actually hit the lowlevel filesystem
for the locking to even trigger in the first place).
I guess some "concurrent readdir with unlink" load would show that
behavior, but is it _realistic_? No idea. Let's not worry about it too
much until somebody shows a reason to worry.
Linus
next prev parent reply other threads:[~2016-06-06 21:20 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-06 20:00 performance delta after VFS i_mutex=>i_rwsem conversion Dave Hansen
2016-06-06 20:46 ` Linus Torvalds
2016-06-06 21:13 ` Waiman Long
2016-06-06 21:20 ` Linus Torvalds [this message]
2016-06-07 3:22 ` Valdis.Kletnieks
2016-06-07 15:22 ` Waiman Long
2016-06-08 8:58 ` Ingo Molnar
2016-06-09 10:25 ` Ingo Molnar
2016-06-09 18:14 ` Dave Hansen
2016-06-09 20:10 ` Chen, Tim C
2016-06-06 21:15 ` Al Viro
2016-06-06 21:46 ` Linus Torvalds
2016-06-06 22:07 ` Al Viro
2016-06-06 23:50 ` Linus Torvalds
2016-06-06 23:59 ` Linus Torvalds
2016-06-07 0:29 ` Linus Torvalds
2016-06-07 0:40 ` Al Viro
2016-06-07 0:44 ` Al Viro
2016-06-07 0:58 ` Al Viro
2016-06-07 0:58 ` Linus Torvalds
2016-06-07 1:19 ` Al Viro
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