Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757732AbaAJQIn (ORCPT ); Fri, 10 Jan 2014 11:08:43 -0500 Received: from smtp.citrix.com ([66.165.176.89]:64582 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751294AbaAJQIj (ORCPT ); Fri, 10 Jan 2014 11:08:39 -0500 X-IronPort-AV: E=Sophos;i="4.95,639,1384300800"; d="scan'208";a="91726545" Date: Fri, 10 Jan 2014 16:08:31 +0000 From: Wei Liu To: David Vrabel CC: Zoltan Kiss , Wei Liu , , , , , Subject: Re: [Xen-devel] [PATCH net-next v3 2/9] xen-netback: Change TX path from grant copy to mapping Message-ID: <20140110160830.GG30581@zion.uk.xensource.com> References: <1389139818-24458-1-git-send-email-zoltan.kiss@citrix.com> <1389139818-24458-3-git-send-email-zoltan.kiss@citrix.com> <20140109153015.GF12164@zion.uk.xensource.com> <52CFDAEC.5080708@citrix.com> <20140110114534.GE29180@zion.uk.xensource.com> <52D01094.5060102@citrix.com> <52D0198C.6000600@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <52D0198C.6000600@citrix.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 10, 2014 at 04:02:20PM +0000, David Vrabel wrote: > On 10/01/14 15:24, Zoltan Kiss wrote: > > On 10/01/14 11:45, Wei Liu wrote: > >> On Fri, Jan 10, 2014 at 11:35:08AM +0000, Zoltan Kiss wrote: > >> [...] > >>> > >>>>> @@ -920,6 +852,18 @@ static int xenvif_tx_check_gop(struct xenvif > >>>>> *vif, > >>>>> err = gop->status; > >>>>> if (unlikely(err)) > >>>>> xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_ERROR); > >>>>> + else { > >>>>> + if (vif->grant_tx_handle[pending_idx] != > >>>>> + NETBACK_INVALID_HANDLE) { > >>>>> + netdev_err(vif->dev, > >>>>> + "Stale mapped handle! pending_idx %x handle %x\n", > >>>>> + pending_idx, vif->grant_tx_handle[pending_idx]); > >>>>> + BUG(); > >>>>> + } > >>>>> + set_phys_to_machine(idx_to_pfn(vif, pending_idx), > >>>>> + FOREIGN_FRAME(gop->dev_bus_addr >> PAGE_SHIFT)); > >>>> > >>>> What happens when you don't have this? > >>> Your frags will be filled with garbage. I don't understand exactly > >>> what this function does, someone might want to enlighten us? I've > >>> took it's usage from classic kernel. > >>> Also, it might be worthwhile to check the return value and BUG if > >>> it's false, but I don't know what exactly that return value means. > >>> > >> > >> This is actually part of gnttab_map_refs. As you're using hypercall > >> directly this becomes very fragile. > >> > >> So the right thing to do is to fix gnttab_map_refs. > > I agree, as I mentioned in other email in this thread, I think that > > should be the topic of an another patchseries. In the meantime, I will > > use gnttab_batch_map instead of the direct hypercall, it handles the > > GNTST_eagain scenario, and I will use set_phys_to_machine the same way > > as m2p_override does: > > If the grant table code doesn't provide the API calls you need you can > either: > > a) add the new API as a prerequisite patch. > b) use the existing API calls and live with the performance problem, > until you can refactor the API later on. > > Adding a netback-specific hack isn't a valid option. > Agreed. Wei. > David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/