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Wed, 27 May 2020 09:53:32 -0700 (PDT) Date: Wed, 27 May 2020 12:53:30 -0400 From: Peter Xu To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened Message-ID: <20200527165330.GG1194141@xz-x1> References: <20200526173542.28710-1-philmd@redhat.com> <6c7c445d-0335-f67d-bb72-5b0c046bb247@redhat.com> <24f88212-9b32-b6dc-fcd4-685cde8bf5d7@redhat.com> <864ac8ab-e21e-393e-d1eb-08b3c4579bbf@redhat.com> <20200527161603.GF1194141@xz-x1> <3e364895-e5e5-09fe-ee8c-782f3632e2b8@redhat.com> MIME-Version: 1.0 In-Reply-To: <3e364895-e5e5-09fe-ee8c-782f3632e2b8@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.120; envelope-from=peterx@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/27 00:49:35 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Auger Eric , Alex Williamson , Cornelia Huck , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, May 27, 2020 at 06:27:38PM +0200, Philippe Mathieu-Daudé wrote: > On 5/27/20 6:16 PM, Peter Xu wrote: > > On Wed, May 27, 2020 at 05:53:16PM +0200, Philippe Mathieu-Daudé wrote: > >>>>> + for (i = 0; i < ARRAY_SIZE(iommu); i++) { > >>>>> + if (ioctl(container->fd, VFIO_CHECK_EXTENSION, iommu[i].type)) { > >>>>> + trace_vfio_get_iommu_type(iommu[i].type, iommu[i].name); > >>>> Just wondering why you want to trace the type as you now have the name > >>>> string. > >>> > >>> You are right :) > >>> > >>>>> + return iommu[i].type; > >>>>> } > >>>>> } > >>>>> + trace_vfio_get_iommu_type(-1, "Not available or not supported"); > >>>> nit: from a debugging pov, this may be not needed as > >>>> vfio_get_group/vfio_connect_container() fails and this leads to an error > >>>> output. > >> > >> But you can reach this for example using No-IOMMU. If you don't mind, I > >> find having this information in the trace log clearer. > > > > I kinda agree with Eric - AFAICT QEMU vfio-pci don't work with no-iommu, then > > it seems meaningless to trace it... > > > > I'm not sure whether this trace is extremely helpful because syscalls like this > > could be easily traced by things like strace or bpftrace as general tools (and > > this information should be a one-time thing rather than dynamically changing), > > no strong opinion though. Also, if we want to dump something, maybe it's > > better to do in vfio_init_container() after vfio_get_iommu_type() succeeded, so > > we dump which container is enabled with what type of iommu. > > OK. I'm a recent VFIO user so maybe I am not using the good information. > > This trace helps me while working on a new device feature, I didn't > thought about gathering it in a production because there I'd expect > things to work. > > Now in my case what I want is to know is if I'm using a v1 or v2 type. > Maybe this information is already available in /proc or /sys and we > don't need this patch... I don't know such /proc or /sys, so maybe it's still useful. I guess Alex would have the best judgement. The strace/bpftrace things are not really reasons I found to nak this patch, but just something I thought first that could be easier when any of us wants to peak at those information, probably something just FYI. :-) Thanks, -- Peter Xu