From owner-freebsd-arch@FreeBSD.ORG  Fri Jun 29 00:36:00 2007
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
X-Original-To: arch@freebsd.org
Delivered-To: freebsd-arch@FreeBSD.ORG
Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52])
	by hub.freebsd.org (Postfix) with ESMTP id 74DBC16A421
	for <arch@freebsd.org>; Fri, 29 Jun 2007 00:36:00 +0000 (UTC)
	(envelope-from davidxu@freebsd.org)
Received: from freefall.freebsd.org (freefall.freebsd.org [69.147.83.40])
	by mx1.freebsd.org (Postfix) with ESMTP id 2B1C713C45A;
	Fri, 29 Jun 2007 00:36:00 +0000 (UTC)
	(envelope-from davidxu@freebsd.org)
Received: from [127.0.0.1] (root@localhost [127.0.0.1])
	by freefall.freebsd.org (8.13.4/8.13.4) with ESMTP id l5T0Zwru042982;
	Fri, 29 Jun 2007 00:35:59 GMT (envelope-from davidxu@freebsd.org)
Message-ID: <46845414.609@freebsd.org>
Date: Fri, 29 Jun 2007 08:36:36 +0800
From: David Xu <davidxu@freebsd.org>
User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.13) Gecko/20070516
X-Accept-Language: en-us, en
MIME-Version: 1.0
To: Jeff Roberson <jroberson@chesapeake.net>
References: <20070628123314.W552@10.0.0.1>
In-Reply-To: <20070628123314.W552@10.0.0.1>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
Cc: arch@freebsd.org
Subject: Re: Add wakeup_with() before 7.0?
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussion related to FreeBSD architecture <freebsd-arch.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch>
List-Post: <mailto:freebsd-arch@freebsd.org>
List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 29 Jun 2007 00:36:00 -0000

Jeff Roberson wrote:
> I propose to add a new api for wakeup before 7.0.  This new api would 
> accept a wait channel and a flags argument.  here's the relevant part of 
> the diff:
> 
> +void   wakeup_with(void *chan, int flags) __nonnull(1);
> +#define        WAKEUP_ONE      0x00001         /* Only wakeup on 
> thread. */
> +#define        WAKEUP_ALL      0x00002         /* Wake-up all waiters. */
> +#define        WAKEUP_LOCAL    0x00004         /* Wake-up on the local 
> cpu. */
> +#define        WAKEUP_TAIL     0x00008         /* Wake-up the newest 
> waiter. */
> 
> This allows wakeup callers to hint the scheduler about various 
> information.  WAKEUP_LOCAL would allow us to prefer affinity for the 
> waking cpu.  I have patches to use this in pipe code and socket buffer 
> code that improve performance in some workloads.  WAKEUP_TAIL could be 
> used for accept() which I have heard can significantly improve webserver 
> performance.
> 

Add my 1 cent here, AFAIK WAKEUP_LOCAL means the current thread will
sleep or give up cpu soon, so there is no needs to wake up a thread
on another cpu, right ?

> To implement this change sched_wakeup() and setrunnable() need the flags 
> plummed all the way through.  I would like feedback on whether people 
> think the api breakage should go in now to enable these optimizations 
> for 7.0, potentially without committing users of these flags right away. 
> Alternatively we could break the api later or just skip it until 8.0.
> 
> Thanks,
> Jeff