From owner-freebsd-current@FreeBSD.ORG  Thu Mar 12 17:08:26 2015
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id 2DB5CEE4;
 Thu, 12 Mar 2015 17:08:26 +0000 (UTC)
Received: from mail-ie0-x234.google.com (mail-ie0-x234.google.com
 [IPv6:2607:f8b0:4001:c03::234])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (Client CN "smtp.gmail.com",
 Issuer "Google Internet Authority G2" (verified OK))
 by mx1.freebsd.org (Postfix) with ESMTPS id E6C73A12;
 Thu, 12 Mar 2015 17:08:25 +0000 (UTC)
Received: by iecvj10 with SMTP id vj10so47897472iec.0;
 Thu, 12 Mar 2015 10:08:25 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113;
 h=mime-version:in-reply-to:references:date:message-id:subject:from:to
 :cc:content-type;
 bh=7YAm0hPkFT+yDSppCdgOz3ngByT0o4+D2oljCaLKe7Y=;
 b=o8LxSmd3k4suhWDeXgd0hgj3Nq5c7J6Hk0+o0IaFXPpk6Fm6ZvlsqiK2VseqfHZg/B
 y8rpJlJ3agIE/daS1Sesy+rCpV/eV7Hzx337XKe5piWLUXaTRrbQw+PklQcIopcl0xfu
 ni/n6X/BNLUXrsmQR92Qe3v854HO/uPln8SYfdUBEz10jW+3A6wRwjXkonFRjt90ruJF
 IniPw7CklcO5nSgM5udS696det9i5JzTL+XrQcLTjU7/K0RXY+50AcwnRme6SgACvC3Q
 MGtgBc26PDeTjhZhSdOmEBa22KJDNxzr6lOQ6YyQKoeR2DF45RwjM2oC0xxAVhZ0ErT6
 l+sA==
MIME-Version: 1.0
X-Received: by 10.50.111.202 with SMTP id ik10mr75937666igb.37.1426180105445; 
 Thu, 12 Mar 2015 10:08:25 -0700 (PDT)
Received: by 10.107.156.75 with HTTP; Thu, 12 Mar 2015 10:08:25 -0700 (PDT)
In-Reply-To: <CAJ-Vmo=-vbKqLdkJCs+9pMrOVysFCx=iAJphMFLFyZNL38M3eQ@mail.gmail.com>
References: <CAFMmRNysnUezX9ozGrCpivPCTMYRJtoxm9ijR0yQO03LpXnwBQ@mail.gmail.com>
 <CAJ-Vmo=-vbKqLdkJCs+9pMrOVysFCx=iAJphMFLFyZNL38M3eQ@mail.gmail.com>
Date: Thu, 12 Mar 2015 13:08:25 -0400
Message-ID: <CAFMmRNzD30SspUUuNNKP7Y1zHaA2t_DcGBg6qhnK0GvzLGQjXw@mail.gmail.com>
Subject: Re: [PATCH] Convert the VFS cache lock to an rmlock
From: Ryan Stone <rysto32@gmail.com>
To: Adrian Chadd <adrian@freebsd.org>
Content-Type: text/plain; charset=UTF-8
X-Content-Filtered-By: Mailman/MimeDel 2.1.18-1
Cc: FreeBSD Current <freebsd-current@freebsd.org>
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.18-1
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
 <freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-current>, 
 <mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current/>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
 <mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 12 Mar 2015 17:08:26 -0000

On Thu, Mar 12, 2015 at 12:37 PM, Adrian Chadd <adrian@freebsd.org> wrote:
> Do you have access to any boxes that have more than 12 cores?

I have a 14-core hyperthreaded machine (so 28 logical cores), but it has no
disk (long story).  I could do a build out of a memory disk though.

Also, to ask a stupid question - why wasn't the reader gifted a
> temporary priority boost because you were trying to acquire the write
> lock?
>

rwlocks don't have any metadata tracking what threads hold a read lock, so
it's impossible to propagate priority to them.  rwlocks only keep a counter
of the number of readers.