From: Eduardo Habkost <ehabkost@redhat.com>
To: Peter Xu <peterx@redhat.com>
Cc: "Daniel P . Berrangé" <berrange@redhat.com>,
"Michael S . Tsirkin" <mst@redhat.com>,
"Jason Wang" <jasowang@redhat.com>,
qemu-devel@nongnu.org, "Markus Armbruster" <armbru@redhat.com>,
"Eric Auger" <eric.auger@redhat.com>,
"Alex Williamson" <alex.williamson@redhat.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: [PATCH 4/4] vl: Prioritize realizations of devices
Date: Mon, 23 Aug 2021 17:56:23 -0400 [thread overview]
Message-ID: <20210823215623.bagyo3oojdpk3byj@habkost.net> (raw)
In-Reply-To: <YSQTwth0elaz4T8W@t490s>
On Mon, Aug 23, 2021 at 05:31:46PM -0400, Peter Xu wrote:
> On Mon, Aug 23, 2021 at 05:07:03PM -0400, Eduardo Habkost wrote:
> > To give just one example:
> >
> > $ (echo 'info pci';echo quit;) | qemu-system-x86_64 -device virtio-net-pci -device e1000e -monitor stdio | tail -n 20
> > Bus 0, device 4, function 0:
> > Ethernet controller: PCI device 1af4:1000
> > PCI subsystem 1af4:0001
> > IRQ 0, pin A
> > BAR0: I/O at 0xffffffffffffffff [0x001e].
> > BAR1: 32 bit memory at 0xffffffffffffffff [0x00000ffe].
> > BAR4: 64 bit prefetchable memory at 0xffffffffffffffff [0x00003ffe].
> > BAR6: 32 bit memory at 0xffffffffffffffff [0x0003fffe].
> > id ""
> > Bus 0, device 5, function 0:
> > Ethernet controller: PCI device 8086:10d3
> > PCI subsystem 8086:0000
> > IRQ 0, pin A
> > BAR0: 32 bit memory at 0xffffffffffffffff [0x0001fffe].
> > BAR1: 32 bit memory at 0xffffffffffffffff [0x0001fffe].
> > BAR2: I/O at 0xffffffffffffffff [0x001e].
> > BAR3: 32 bit memory at 0xffffffffffffffff [0x00003ffe].
> > BAR6: 32 bit memory at 0xffffffffffffffff [0x0003fffe].
> > id ""
> > (qemu) quit
> > $ (echo 'info pci';echo quit;) | qemu-system-x86_64 -device e1000e -device virtio-net-pci -monitor stdio | tail -n 20
> > Bus 0, device 4, function 0:
> > Ethernet controller: PCI device 8086:10d3
> > PCI subsystem 8086:0000
> > IRQ 0, pin A
> > BAR0: 32 bit memory at 0xffffffffffffffff [0x0001fffe].
> > BAR1: 32 bit memory at 0xffffffffffffffff [0x0001fffe].
> > BAR2: I/O at 0xffffffffffffffff [0x001e].
> > BAR3: 32 bit memory at 0xffffffffffffffff [0x00003ffe].
> > BAR6: 32 bit memory at 0xffffffffffffffff [0x0003fffe].
> > id ""
> > Bus 0, device 5, function 0:
> > Ethernet controller: PCI device 1af4:1000
> > PCI subsystem 1af4:0001
> > IRQ 0, pin A
> > BAR0: I/O at 0xffffffffffffffff [0x001e].
> > BAR1: 32 bit memory at 0xffffffffffffffff [0x00000ffe].
> > BAR4: 64 bit prefetchable memory at 0xffffffffffffffff [0x00003ffe].
> > BAR6: 32 bit memory at 0xffffffffffffffff [0x0003fffe].
> > id ""
> > (qemu) quit
> >
> >
> > If the order of the -device arguments changes, the devices are assigned to
> > different PCI slots.
>
> Thanks for the example.
>
> Initially I thought about this and didn't think it an issue (because serious
> users will always specify addr=XXX for -device; I thought libvirt always does
> that), but I do remember that guest OS could identify its hardware config with
> devfn number, so nmcli may mess up its config with before/after this change
> indeed..
>
> I can use a custom sort to replace qsort() to guarantee that.
>
> Do you have other examples in mind that I may have overlooked, especially I may
> not be able to fix by a custom sort with only moving priority>=1 devices?
I don't have any other example, but I assume address assignment
based on ordering is a common pattern in device code.
I would take a very close and careful look at the devices with
non-default vmsd priority. If you can prove that the 13 device
types with non-default priority are all order-insensitive, a
custom sort function as you describe might be safe.
--
Eduardo
next prev parent reply other threads:[~2021-08-23 21:57 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-18 19:42 [PATCH 0/4] vl: Prioritize device realizations Peter Xu
2021-08-18 19:42 ` [PATCH 1/4] qdev-monitor: Trace qdev creation Peter Xu
2021-08-18 19:43 ` [PATCH 2/4] qemu-config: Allow in-place sorting of QemuOptsList Peter Xu
2021-08-18 19:43 ` [PATCH 3/4] qdev: Export qdev_get_device_class() Peter Xu
2021-08-18 19:43 ` [PATCH 4/4] vl: Prioritize realizations of devices Peter Xu
2021-08-23 18:49 ` Eduardo Habkost
2021-08-23 19:18 ` Peter Xu
2021-08-23 21:07 ` Eduardo Habkost
2021-08-23 21:31 ` Peter Xu
2021-08-23 21:54 ` Michael S. Tsirkin
2021-08-23 22:51 ` Peter Xu
2021-08-23 21:56 ` Eduardo Habkost [this message]
2021-08-23 23:05 ` Peter Xu
2021-08-25 9:39 ` Markus Armbruster
2021-08-25 12:28 ` Markus Armbruster
2021-08-25 21:50 ` Peter Xu
2021-08-26 3:50 ` Peter Xu
2021-08-26 8:01 ` Markus Armbruster
2021-08-26 11:36 ` Igor Mammedov
2021-08-26 13:43 ` Peter Xu
2021-08-30 19:02 ` Peter Xu
2021-08-31 11:35 ` Markus Armbruster
2021-09-02 8:26 ` Igor Mammedov
2021-09-02 13:45 ` Peter Xu
2021-09-02 13:53 ` Daniel P. Berrangé
2021-09-02 14:21 ` Peter Xu
2021-09-02 14:57 ` Markus Armbruster
2021-09-03 15:48 ` Peter Xu
2021-09-02 15:06 ` Daniel P. Berrangé
2021-09-02 15:26 ` Markus Armbruster
2021-09-03 13:00 ` Igor Mammedov
2021-09-03 16:03 ` Peter Xu
2021-09-06 8:49 ` Igor Mammedov
2021-09-02 7:46 ` Igor Mammedov
2021-08-26 4:57 ` Markus Armbruster
2021-08-23 22:05 ` Michael S. Tsirkin
2021-08-23 22:36 ` Peter Xu
2021-08-24 2:52 ` Jason Wang
2021-08-24 15:50 ` Peter Xu
2021-08-25 4:23 ` Jason Wang
2021-09-06 9:22 ` Eric Auger
2021-08-24 16:24 ` David Hildenbrand
2021-08-24 19:52 ` Peter Xu
2021-08-25 8:08 ` David Hildenbrand
2021-08-24 2:51 ` Jason Wang
2021-10-20 13:44 ` [PATCH 0/4] vl: Prioritize device realizations David Hildenbrand
2021-10-20 13:48 ` Daniel P. Berrangé
2021-10-20 13:58 ` David Hildenbrand
2021-10-21 4:20 ` Peter Xu
2021-10-21 7:17 ` David Hildenbrand
2021-10-21 8:00 ` Peter Xu
2021-10-21 16:54 ` David Hildenbrand
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