From mboxrd@z Thu Jan 1 00:00:00 1970 From: konrad wilk Subject: Re: [Xen-devel] [PATCH] xen/grant-table: Force to use v1 of grants. Date: Thu, 17 Jan 2013 21:32:35 -0500 Message-ID: <50F8B443.7070704@oracle.com> References: <1358371369-19089-1-git-send-email-konrad.wilk@oracle.com> <20130117110829.GA21859@u109add4315675089e695.ant.amazon.com> <50F8050C02000078000B6D33@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <50F8050C02000078000B6D33@nat28.tlf.novell.com> Sender: linux-kernel-owner@vger.kernel.org To: Jan Beulich Cc: Matt Wilson , xen-devel@lists.xensource.com, annie.li@oracle.com, linux-kernel@vger.kernel.org List-Id: xen-devel@lists.xenproject.org On 1/17/2013 8:05 AM, Jan Beulich wrote: >>>> On 17.01.13 at 13:22, Matt Wilson wrote: >> On Wed, Jan 16, 2013 at 04:22:49PM -0500, Konrad Rzeszutek Wilk wrote: >>> We have the framework to use v2, but there are no backends that >>> actually use it. The end result is that on PV we use v2 grants >>> and on PVHVM v1. The v1 has a capacity of 512 grants per page while >>> the v2 has 256 grants per page. This means we lose about 50% >>> capacity - and if we want more than 16 VIFs (each VIF takes >>> 512 grants), then we are hitting the max per guest of 32. >>> >>> Note: The hypervisor provides an over-ride for the default >>> of 32 frames (pages) per guest: gnttab_max_nr_frames=X >> I think it would be better if the dom0/service domain and hypervisor >> prevent the guest from setting the version to 2 if the backend isn't >> going to make use of them. In the short term, we could add a Xen >> option to limit the supported version to 1. > But that's something each guest has to decide for itself. > > Anyway - if no-one's using v2, what did it get introduced for > (not only in the hypervisor, but also in the kernel)? I thought > the networking drivers were intended to make use of it... That was the idea, but the work on that stalled. I think that once the netfront or netback has the right code, then we can revert this patch - or just make this be more automatic and change itself to V2 if it can. > Jan >