linux-kernel - Re: Stupid VFS name lookup interface..

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Date:	Thu, 30 May 2013 12:05:15 +0900
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Eric Paris <eparis@...isplace.org>
Cc:	James Morris <jmorris@...ei.org>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Eric Paris <eparis@...hat.com>,
	James Morris <james.l.morris@...cle.com>
Subject: Re: Stupid VFS name lookup interface..

On Thu, May 30, 2013 at 10:28 AM, Eric Paris <eparis@...isplace.org> wrote:
>
> How do I tell what is taking time inside selinux_inode_permission?

Go to "annotate" (just press 'a' when the function is highlighted),
which will show you the disassembly and the cost of each instruction.

That's when you really want to use "-e cycles:pp" to get the
instruction-level profile right, though. Otherwise the cost will
usually be assigned to the instructions following the expensive one.

And I can tell you that the cost is almost certainly the cache miss on
the inode->i_security accesses. Which was the reason for that second
patch that moved "sid" to the inode->i_sid field and avoided the extra
dereference.

             Linus
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