From owner-cvs-src Sat Mar 8 23:58: 2 2003 Delivered-To: cvs-src@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 674F437B401; Sat, 8 Mar 2003 23:58:01 -0800 (PST) Received: from critter.freebsd.dk (critter.freebsd.dk [212.242.86.163]) by mx1.FreeBSD.org (Postfix) with ESMTP id 8439E43FB1; Sat, 8 Mar 2003 23:58:00 -0800 (PST) (envelope-from phk@phk.freebsd.dk) Received: from critter.freebsd.dk (localhost [127.0.0.1]) by critter.freebsd.dk (8.12.8/8.12.8) with ESMTP id h297vxNw078208; Sun, 9 Mar 2003 08:57:59 +0100 (CET) (envelope-from phk@phk.freebsd.dk) To: Nate Lawson Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: cvs commit: src/sys/sys devicestat.h From: "Poul-Henning Kamp" In-Reply-To: Your message of "Sat, 08 Mar 2003 23:50:06 PST." Date: Sun, 09 Mar 2003 08:57:59 +0100 Message-ID: <78207.1047196679@critter.freebsd.dk> Sender: owner-cvs-src@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In message , Nate Lawson wri tes: >> Yes, these structures will be mmap'ed from kernel to userland and user >> land will (likely) memcpy() them to private storage as snapshot'ing. >> To be able to tell if you have an atomic snapshot, the two counters >> must be identical. > >How about a mtx covering the structure and a read from the device returns >the structure under lock? The goal is to avoid locking in the kernel and put the overhead in userland. Remember, most of the time nobody cares about the statistics so they should be cheap. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-src" in the body of the message