From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH] kvm: Increase NR_IOBUS_DEVS limit to 200 Date: Wed, 31 Mar 2010 12:51:16 +0300 Message-ID: <20100331095116.GF31085@redhat.com> References: <1269992905.29847.35.camel@w-sridhar.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Avi Kivity , "kvm@vger.kernel.org" To: Sridhar Samudrala Return-path: Received: from mx1.redhat.com ([209.132.183.28]:31795 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754937Ab0CaJyv (ORCPT ); Wed, 31 Mar 2010 05:54:51 -0400 Content-Disposition: inline In-Reply-To: <1269992905.29847.35.camel@w-sridhar.beaverton.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Mar 30, 2010 at 04:48:25PM -0700, Sridhar Samudrala wrote: > This patch increases the current hardcoded limit of NR_IOBUS_DEVS > from 6 to 200. We are hitting this limit when creating a guest with more > than 1 virtio-net device using vhost-net backend. Each virtio-net > device requires 2 such devices to service notifications from rx/tx queues. > > Signed-off-by: Sridhar Samudrala > I tried this, but observed a measurable performance degradation with vhost net and this patch. Did not investigate yet. Do you see this as well? > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index a3fd0f9..7fb48d3 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -54,7 +54,7 @@ extern struct kmem_cache *kvm_vcpu_cache; > */ > struct kvm_io_bus { > int dev_count; > -#define NR_IOBUS_DEVS 6 > +#define NR_IOBUS_DEVS 200 > struct kvm_io_device *devs[NR_IOBUS_DEVS]; > }; > > >