From owner-freebsd-hackers Wed Aug 19 09:51:41 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id JAA13519 for freebsd-hackers-outgoing; Wed, 19 Aug 1998 09:51:41 -0700 (PDT) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from redfish.go2net.com (redfish.go2net.com [207.178.55.5]) by hub.freebsd.org (8.8.8/8.8.8) with SMTP id JAA13513 for ; Wed, 19 Aug 1998 09:51:39 -0700 (PDT) (envelope-from marcs@go2net.com) Received: from marcs by redfish.go2net.com with smtp (Exim 1.82 #2) id 0z9BQd-0003sa-00; Wed, 19 Aug 1998 09:49:43 -0700 Date: Wed, 19 Aug 1998 09:49:43 -0700 (PDT) From: Marc Slemko X-Sender: marcs@redfish To: Wolfram Schneider cc: hackers@FreeBSD.ORG Subject: Re: sendfile() API? In-Reply-To: <19980819111809.A22887@caramba.cs.tu-berlin.de> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Wed, 19 Aug 1998, Wolfram Schneider wrote: > On 1998-08-17 18:17:34 +0000, Terry Lambert wrote: > > I have no doubt that it would be useful for static pages; I am just not > > convinced that pushing the data over a call boundary is the real overhead > > here. For an mmap'ed file, the only overhead is the copy from the VM > > buffer to the mbuf. The only way such a call could eliminated this > > overhead is by passing the VM buffers down as mbuf contents. This can > > be done (I did the code for it on the VMS NetWare server), but it's > > a lot of work. > > Who cares about data copy overhead? If the kernel spend 5% of the CPU > time in copying, there are still 95% free CPU cycles. > > Freefall.freebsd.org transfers 20KB/s with a CPU load less > than 0.01. Lots of people do and should care about it. freefall has such a tiny amount of web traffic that you could add an extra dozen copies to the path without it mattering. However, as you scale upwards by a few orders of magnitude, a bottleneck clearly appears on most current systems where you have excessive copying. Not all of this can be reflected in the CPU use of the process. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message