Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757984AbaAJQEj (ORCPT ); Fri, 10 Jan 2014 11:04:39 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:36942 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757959AbaAJQEe (ORCPT ); Fri, 10 Jan 2014 11:04:34 -0500 X-IronPort-AV: E=Sophos;i="4.95,639,1384300800"; d="scan'208";a="89584296" Message-ID: <52D0198C.6000600@citrix.com> Date: Fri, 10 Jan 2014 16:02:20 +0000 From: David Vrabel User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20121215 Iceowl/1.0b1 Icedove/3.0.11 MIME-Version: 1.0 To: Zoltan Kiss CC: Wei Liu , , , , , Subject: Re: [Xen-devel] [PATCH net-next v3 2/9] xen-netback: Change TX path from grant copy to mapping 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> In-Reply-To: <52D01094.5060102@citrix.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.76] X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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/