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Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened
From: |
Cornelia Huck |
Subject: |
Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened |
Date: |
Wed, 27 May 2020 19:06:51 +0200 |
On Wed, 27 May 2020 12:53:30 -0400
Peter Xu <address@hidden> wrote:
> 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. :-)
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 :)
- [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened, Philippe Mathieu-Daudé, 2020/05/26
- Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened, Cornelia Huck, 2020/05/27
- Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened, Auger Eric, 2020/05/27
- Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened, Philippe Mathieu-Daudé, 2020/05/27
- Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened, Philippe Mathieu-Daudé, 2020/05/27
- Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened, Peter Xu, 2020/05/27
- Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened, Philippe Mathieu-Daudé, 2020/05/27
- Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened, Peter Xu, 2020/05/27
- Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened,
Cornelia Huck <=
- Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened, Peter Xu, 2020/05/27
- Re: [PATCH] hw/vfio/common: Trace in which mode a IOMMU is opened, Alex Williamson, 2020/05/28