Re: [PATCH 4/4] vl: Prioritize realizations of devices

From: Peter Xu <peterx@redhat.com>
To: Eduardo Habkost <ehabkost@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 17:31:46 -0400	[thread overview]
Message-ID: <YSQTwth0elaz4T8W@t490s> (raw)
In-Reply-To: <20210823210703.cikdkhvyeqqypaqa@habkost.net>

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?

Thanks,

-- 
Peter Xu