From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39997) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZTgc9-0003s1-0S for qemu-devel@nongnu.org; Sun, 23 Aug 2015 21:31:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZTgc5-0004iv-Rq for qemu-devel@nongnu.org; Sun, 23 Aug 2015 21:31:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37270) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZTgc5-0004im-ND for qemu-devel@nongnu.org; Sun, 23 Aug 2015 21:31:53 -0400 References: <1440375847-17603-1-git-send-email-cota@braap.org> <1440375847-17603-39-git-send-email-cota@braap.org> From: Paolo Bonzini Message-ID: <55DA7396.3060300@redhat.com> Date: Sun, 23 Aug 2015 18:29:58 -0700 MIME-Version: 1.0 In-Reply-To: <1440375847-17603-39-git-send-email-cota@braap.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC 38/38] Revert "target-i386: yield to another VCPU on PAUSE" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Emilio G. Cota" , qemu-devel@nongnu.org, mttcg@greensocs.com Cc: guillaume.delbergue@greensocs.com, alex.bennee@linaro.org, mark.burton@greensocs.com, a.rigo@virtualopensystems.com, Frederic Konrad On 23/08/2015 17:24, Emilio G. Cota wrote: > This reverts commit 81f3053b77f7d3a4d9100c425cd8cec99ee7a3d4. > > The interrupt raised by the change in the commit above > kills performance when running many idling VCPUs. For example, > on my 64-core host when running a workload where cores are > idling often (e.g. blackscholes), performance drops significantly > because threads are most of the time just exiting the CPU loop, > thereby causing great contention on the BQL. > > Fix it by reverting to the old behaviour by which no > interrupt is raised, which shouldn't be an issue given that > we have now one thread per VCPU. > > Signed-off-by: Emilio G. Cota Agreed, this is not necessary anymore! Paolo