From owner-svn-src-head@freebsd.org  Wed Mar 16 04:40:06 2016
Return-Path: <owner-svn-src-head@freebsd.org>
Delivered-To: svn-src-head@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id 31114AD2CA6;
 Wed, 16 Mar 2016 04:40:06 +0000 (UTC)
 (envelope-from julian@freebsd.org)
Received: from vps1.elischer.org (vps1.elischer.org [204.109.63.16])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client CN "vps1.elischer.org",
 Issuer "CA Cert Signing Authority" (not verified))
 by mx1.freebsd.org (Postfix) with ESMTPS id EFC491119;
 Wed, 16 Mar 2016 04:40:05 +0000 (UTC)
 (envelope-from julian@freebsd.org)
Received: from Julian-MBP3.local
 (ppp121-45-229-231.lns20.per1.internode.on.net [121.45.229.231])
 (authenticated bits=0)
 by vps1.elischer.org (8.15.2/8.15.2) with ESMTPSA id u2G4drV5013964
 (version=TLSv1.2 cipher=DHE-RSA-AES128-SHA bits=128 verify=NO);
 Tue, 15 Mar 2016 21:39:56 -0700 (PDT)
 (envelope-from julian@freebsd.org)
Subject: Re: svn commit: r296880 - in head: share/man/man9 sys/kern sys/sys
To: Gleb Smirnoff <glebius@FreeBSD.org>, Ravi Pokala <rpokala@mac.com>
References: <201603150005.u2F050ps086390@repo.freebsd.org>
 <BBC31E16-31C0-426A-96C0-1393CA3DC379@panasas.com>
 <20160315191229.GU1328@FreeBSD.org>
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
From: Julian Elischer <julian@freebsd.org>
Message-ID: <56E8E394.7090100@freebsd.org>
Date: Wed, 16 Mar 2016 12:39:48 +0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:38.0)
 Gecko/20100101 Thunderbird/38.6.0
MIME-Version: 1.0
In-Reply-To: <20160315191229.GU1328@FreeBSD.org>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
X-BeenThere: svn-src-head@freebsd.org
X-Mailman-Version: 2.1.21
Precedence: list
List-Id: SVN commit messages for the src tree for head/-current
 <svn-src-head.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/svn-src-head>,
 <mailto:svn-src-head-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-head/>
List-Post: <mailto:svn-src-head@freebsd.org>
List-Help: <mailto:svn-src-head-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/svn-src-head>,
 <mailto:svn-src-head-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 16 Mar 2016 04:40:06 -0000

On 16/03/2016 3:12 AM, Gleb Smirnoff wrote:
>    Ravi,
>
> On Mon, Mar 14, 2016 at 05:33:06PM -0700, Ravi Pokala wrote:
> R> To make sure I'm reading this correctly:
> R>
> R> (1) The sysctl operates on an opaque array of (uint64_t)s. The elements of the array are not individually accessible.
>
> On array of counter_u64_t. The elements are individually accessible of course,
> but not by this sysctl API.
>
> R> (2) Reading the sysctl populates each element of the userspace array by calling counter_u64_fetch() on the corresponding element of the kernelspace array.
>
> Right.
>
> R> (3) Writing the sysctl clears the kernelspace array by calling counter_u64_zero() on each element.
>
> Right.
>
but it is not atomic.  since the user process decides the time delay 
between a read and write (zero) there could be  a lot of missed counts 
if you are resetting to zero after each read. better to just read in a 
loop and not zero..
here are somethings I've wanted at various times:
   read/zero atomic
   read timestamp as part of imported struct. (because you really 
can't do accurate timing from user space, but knowing when the data 
was read is a good replacement).
  read a "mib" (for want of a better term)  for each set, giving 
individual field names.