From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756154Ab2DQOs2 (ORCPT ); Tue, 17 Apr 2012 10:48:28 -0400 Received: from acsinet15.oracle.com ([141.146.126.227]:19875 "EHLO acsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755802Ab2DQOs0 (ORCPT ); Tue, 17 Apr 2012 10:48:26 -0400 Date: Tue, 17 Apr 2012 10:43:19 -0400 From: Konrad Rzeszutek Wilk To: Stefano Stabellini Cc: "xen-devel@lists.xensource.com" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v3 1/2] xen: enter/exit lazy_mmu_mode around m2p_override calls Message-ID: <20120417144318.GA28477@phenom.dumpdata.com> References: <1334075375-25442-1-git-send-email-stefano.stabellini@eu.citrix.com> <20120417130340.GA25593@phenom.dumpdata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: acsinet22.oracle.com [141.146.126.238] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090205.4F8D82B4.00BE,ss=1,re=0.000,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 17, 2012 at 03:26:05PM +0100, Stefano Stabellini wrote: > On Tue, 17 Apr 2012, Konrad Rzeszutek Wilk wrote: > > On Tue, Apr 10, 2012 at 05:29:34PM +0100, Stefano Stabellini wrote: > > > This patch is a significant performance improvement for the > > > m2p_override: about 6% using the gntdev device. > > > > > > Each m2p_add/remove_override call issues a MULTI_grant_table_op and a > > > __flush_tlb_single if kmap_op != NULL. Batching all the calls together > > > is a great performance benefit because it means issuing one hypercall > > > total rather than two hypercall per page. > > > If paravirt_lazy_mode is set PARAVIRT_LAZY_MMU, all these calls are > > > going to be batched together, otherwise they are issued one at a time. > > > > > > Adding arch_enter_lazy_mmu_mode/arch_leave_lazy_mmu_mode around the > > > m2p_add/remove_override calls forces paravirt_lazy_mode to > > > PARAVIRT_LAZY_MMU, therefore makes sure that they are always batched. > > > > > > > > > Changes in v3: > > > - do not call arch_enter/leave_lazy_mmu_mode in xen_blkbk_unmap, that > > > can be called in interrupt context. > > > > This is with RHEL5 (somehow the pvops kernels don't trigger this): > > Do you mean RHEL5 as a guest? Are you using blkback or qdisk? blkback: memory = 1024 name = "RHEL5-64" hvm_loader="/usr/bin/pygrub" vfb = [ 'vnc=1, vnclisten=0.0.0.0,vncunused=1'] vcpus=2 vif = [ ' mac=00:0F:4B:00:00:74,bridge=switch' ] disk = [ 'phy:/dev/guests/RHEL5-64,xvda,w' ] boot = "dnc" device_model = 'qemu-dm' vnc=1 videoram=8 vnclisten="0.0.0.0" vncpasswd='' stdvga=0 serial='pty' tsc_mode=0 usb=1 usbdevice='tablet' xen_platform_pci=1 Thought looking at that guest config I am not sure what it boots as anymore :-( > How can I repro the bug? I just bootup the RHEL5 guest and when it tries to get an DHCP address it then blows up. Hm, maybe the issue is with network - tap vs netfront ? > > > In any case it looks like a similar kind of issue to the one I fixed > before: paravirt_enter_lazy_mmu is probably called with > paravirt_lazy_mode == PARAVIRT_LAZY_MMU, in this case by > gnttab_unmap_refs. > But I don't understand how gnttab_unmap_refs can be called when you seem > to be using blkback. > > Anyhow gnttab_unmap_refs can be called by: > > - mmu_notifier on invalidate_range_start; > - vm_operations_struct on close; > - file_operations on release; > - the unmap gntdev ioctl. > > I guess the mmu_notifier or vm_operations_struct could be the ones > calling gnttab_unmap_refs with lazy_mode set to PARAVIRT_LAZY_MMU. > > I suspect that something like the following code would fix the issue but > it is pretty ugly and I need to test it before a submitting it as a fix: > > > @@ -780,7 +780,7 @@ EXPORT_SYMBOL_GPL(gnttab_map_refs); > int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops, > struct page **pages, unsigned int count, bool clear_pte) > { > - int i, ret; > + int i, ret, lazy = 0; > > ret = HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, unmap_ops, count); > if (ret) > > @@ -789,7 +789,10 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops, > if (xen_feature(XENFEAT_auto_translated_physmap)) > return ret; > > - arch_enter_lazy_mmu_mode(); > + if (!in_interrupt() && paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) { > + arch_enter_lazy_mmu_mode(); > + lazy = 1; > + } > > for (i = 0; i < count; i++) { > ret = m2p_remove_override(pages[i], clear_pte); > @@ -797,7 +800,8 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops, > return ret; > } > > - arch_leave_lazy_mmu_mode(); > + if (lazy) > + arch_leave_lazy_mmu_mode(); > > return ret; > }