linux-kernel - Re: [PATCH 10/11] ring-buffer: move big if statement down

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.00.0905060930190.3239@gandalf.stny.rr.com>
Date:	Wed, 6 May 2009 09:47:34 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 10/11] ring-buffer: move big if statement down


On Wed, 6 May 2009, Ingo Molnar wrote:

> 
> * Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > This patch changes it to a goto:
> > 
> > 	code;
> > 
> > 	if (cross to next page)
> > 		goto next_page;
> > 
> > 	more code;
> > 
> > 	return;
> > 
> > next_page:
> > 
> > 	[ lots of code]
> 
> I have pulled it, but could you please change it to a helper 
> function instead? There's almost never a good reason to combine 
> 'more code' with 'lots of code' in a single function. It also 
> documents the unlikeliness, etc.

As I stated in the change log, I did not want to convert it to a helper 
function because it uses the variables created before. It would end up 
going from:

	if (write > BUF_PAGE_SIZE)
		goto next_page;


to:

	if (write > BUF_PAGE_SIZE)
		return rb_move_tail(cpu_buffer, length, tail,
				    commit_page, tail_page);


Although it is the "unlikely" case, it is still a fast path. It happens 
every time a write into the page buffer crosses a page boundary. Since it 
is only used once, gcc would hopefully inline it. If it does not, then we 
are copying a bunch of parameters for nothing.

I could still do this and see what gcc does with it.

-- Steve

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/