From owner-freebsd-emulation@FreeBSD.ORG  Thu Dec 13 13:05:04 2012
Return-Path: <owner-freebsd-emulation@FreeBSD.ORG>
Delivered-To: freebsd-emulation@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52])
 by hub.freebsd.org (Postfix) with ESMTP id C0CA7B5A;
 Thu, 13 Dec 2012 13:05:04 +0000 (UTC) (envelope-from avg@FreeBSD.org)
Received: from citadel.icyb.net.ua (citadel.icyb.net.ua [212.40.38.140])
 by mx1.freebsd.org (Postfix) with ESMTP id DC2D98FC12;
 Thu, 13 Dec 2012 13:05:02 +0000 (UTC)
Received: from odyssey.starpoint.kiev.ua (alpha-e.starpoint.kiev.ua
 [212.40.38.101])
 by citadel.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id PAA15779;
 Thu, 13 Dec 2012 15:05:01 +0200 (EET) (envelope-from avg@FreeBSD.org)
Message-ID: <50C9D27C.1090707@FreeBSD.org>
Date: Thu, 13 Dec 2012 15:05:00 +0200
From: Andriy Gapon <avg@FreeBSD.org>
User-Agent: Mozilla/5.0 (X11; FreeBSD amd64;
 rv:17.0) Gecko/17.0 Thunderbird/17.0
MIME-Version: 1.0
To: vbox@FreeBSD.org, freebsd-emulation@FreeBSD.org
Subject: issue with under-tick waits
X-Enigmail-Version: 1.4.6
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-BeenThere: freebsd-emulation@freebsd.org
X-Mailman-Version: 2.1.14
Precedence: list
List-Id: Development of Emulators of other operating systems
 <freebsd-emulation.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-emulation>, 
 <mailto:freebsd-emulation-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-emulation>
List-Post: <mailto:freebsd-emulation@freebsd.org>
List-Help: <mailto:freebsd-emulation-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-emulation>, 
 <mailto:freebsd-emulation-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 13 Dec 2012 13:05:04 -0000


I think that the following patch is needed in VirtualBox 4.2.4 kernel module:

--- sleepqueue-r0drv-freebsd.h.orig	2012-12-12 20:09:29.675203802 +0200
+++ sleepqueue-r0drv-freebsd.h	2012-12-12 20:11:53.604203131 +0200
@@ -82,6 +82,8 @@
     uint64_t cTicks = ASMMultU64ByU32DivByU32(uTimeout, hz, UINT32_C(1000000000));
     if (cTicks >= INT_MAX)
         return RTSEMWAIT_FLAGS_INDEFINITE;
+    else if (cTicks == 0 && uTimeout > 0)
+        pWait->iTimeout     = 1;
     else
         pWait->iTimeout     = (int)cTicks;
 #endif

Without this patch any waits for periods shorter than a single tick return
immediately leading to a lot of unnecessary spinning.  For example, I observe that
my guest's idle loop does a lot of sleeps with periods slightly shorter than 1 ms
(1/hz), e.g. 900us.  All that waiting turns into pure spinning and VirtualBox eats
100% of a core.
The above patch improves the situation significantly.  Also, it (approximately)
follows what tvtohz does.

-- 
Andriy Gapon