linux-kernel - Re: [PATCH] namei: Remove unlikely annotation for revalidate check in lookup

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Message-ID: <20170206203415.1bd33992@grimm.local.home>
Date:   Mon, 6 Feb 2017 20:34:15 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] namei: Remove unlikely annotation for revalidate check
 in lookup_fast()

On Tue, 7 Feb 2017 00:06:42 +0000
Al Viro <viro@...IV.linux.org.uk> wrote:

> On Mon, Feb 06, 2017 at 05:17:35PM -0500, Steven Rostedt wrote:
> > From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> > 
> > The likely/unlikely profiler showed that the unlikely around the
> > dentry->d_flags & DCACHE_OP_REVALIDATE was wrong 95% of the time. Adding
> > trace_printk()s, it revealed that the dentry ops had hooks to:
> > 
> >  kernfs_dop_revalidate
> >  pid_revalidate
> >  proc_sys_revalidate
> >  tid_fd_revalidate
> > 
> > As tools today now access files that have these operations often, it's best
> > just to remove the annotation, as it is more dependent on use cases and not
> > normal mode of operation if it will be true or not.  
> 
> "Tools" being what, exactly?  What kind of load had that been measured on?

I first saw it on my system that I ran for 3 weeks. But I investigated
it more on a test box that was mostly idle. On the test box the "tools"
was mostly systemd and journald. I can look deeper into it if you like.

-- Steve