From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Magenheimer Subject: vsyscalls may be going away... impact on Xen time performance on Linux in the future? Date: Thu, 9 Jun 2011 14:55:16 -0700 (PDT) Message-ID: <070733f8-c7aa-4543-85dd-d353088b0e20@default> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com Cc: jeremy@goop.org, Konrad Wilk List-Id: xen-devel@lists.xenproject.org Hmmm... It appears that Xen time mechanisms that use vsyscall may be getting slower... "This is a significant performance penalty (~220ns here) for all vsyscall users, but there aren't many left." http://lwn.net/Articles/446220/=20 I honestly don't remember all the details myself anymore, but I think this means that user apps in Xen PV domains that call gettimeofday a *lot* may be in for a bit of a shock when they move to a 3.x kernel in the future. (Many enterprise apps do things like timestamp transactions, which can lead to 10s of thousands of gettimeofday's per second.) See the xen-devel discussion here: http://lists.xensource.com/archives/html/xen-devel/2010-10/msg00872.html=20 Dan P.S. For lwn subscribers (or non-subscribers willing to wait a week), see Jonathan Corbet's nice overview at http://lwn.net/Articles/446125/=20 -- Thanks... for the memory! I really could use more / my throughput's on the floor The balloon is flat / my swap disk's fat / I've OOM's in store Overcommitted so much (with apologies to Bob Hope)