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Wed, 27 May 2020 17:06:53 +0000 (UTC) Date: Wed, 27 May 2020 19:06:51 +0200 From: Cornelia Huck To: Peter Xu Subject: Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened Message-ID: <20200527190651.2a9ee6ea.cohuck@redhat.com> In-Reply-To: <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> <20200527165330.GG1194141@xz-x1> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=205.139.110.61; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/27 05:46:19 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_H2=-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 , Philippe =?UTF-8?B?TWF0aGlldS1EYXVkw6k=?= , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 27 May 2020 12:53:30 -0400 Peter Xu wrote: > On Wed, May 27, 2020 at 06:27:38PM +0200, Philippe Mathieu-Daud=C3=A9 wro= te: > > On 5/27/20 6:16 PM, Peter Xu wrote: =20 > > > On Wed, May 27, 2020 at 05:53:16PM +0200, Philippe Mathieu-Daud=C3=A9= wrote: =20 > > >>>>> + for (i =3D 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].na= me); =20 > > >>>> Just wondering why you want to trace the type as you now have the = name > > >>>> string. =20 > > >>> > > >>> You are right :) > > >>> =20 > > >>>>> + return iommu[i].type; > > >>>>> } > > >>>>> } > > >>>>> + trace_vfio_get_iommu_type(-1, "Not available or not supporte= d"); =20 > > >>>> 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. =20 > > >> > > >> 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. =20 > > >=20 > > > I kinda agree with Eric - AFAICT QEMU vfio-pci don't work with no-iom= mu, then > > > it seems meaningless to trace it... > > >=20 > > > 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 t= ools (and > > > this information should be a one-time thing rather than dynamically c= hanging), > > > 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() suc= ceeded, so > > > we dump which container is enabled with what type of iommu. =20 > >=20 > > OK. I'm a recent VFIO user so maybe I am not using the good information= . > >=20 > > 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. > >=20 > > 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... =20 >=20 > 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 reason= s 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 someth= ing > just FYI. :-) Personally, I find traces to be quite handy, and it's nice if you can just enable more of them if they are in your debugging workflow anyway. Probably boils down to a matter of preference :)