CV-Bowen opened a new pull request, #18290:
URL: https://github.com/apache/nuttx/pull/18290
## Summary
This PR optimizes the VirtIO MMIO and PCI interrupt handlers by replacing
direct access to virtqueue internal fields with the proper `virtqueue_nused()`
API.
### Why this change is needed
The current implementation directly accesses virtqueue internal fields
(`vq->vq_used_cons_idx` and `vq->vq_ring.used->idx`) to determine if there are
pending buffers to process. This approach has several issues:
1. **Breaks encapsulation**: Direct field access bypasses the virtqueue
abstraction layer
2. **Cache coherency issues**: The direct comparison doesn't handle cached
memory scenarios properly
3. **Maintainability**: Changes to virtqueue internals would require updates
in multiple places
### What this PR does
- Replaces `vq->vq_used_cons_idx != vq->vq_ring.used->idx` with
`virtqueue_nused(vq) > 0`
- Reorders the condition to check `vq->callback != NULL` first
(short-circuit optimization)
- Applies the same fix to both `virtio-mmio.c` and `virtio-pci.c`
## Impact
- **Stability**: Improves reliability when using cached memory for virtqueues
- **Compatibility**: No API changes, fully backward compatible
- **Code Quality**: Better encapsulation and maintainability
## Testing
### Build Verification
```bash
# Build for qemu-armv8a with virtio support
cmake -B cmake_out -DBOARD_CONFIG=qemu-armv8a:netnsh -GNinja
cmake --build cmake_out
```
### Runtime Testing
Tested on QEMU ARM64 with virtio-net device:
VirtIO-MMIO Test
```c
❯ /data/software/qemu/qemu-9.2.3/build/qemu-system-aarch64 -cpu cortex-a53
-nographic \
-machine virt,virtualization=on,gic-version=3 \
-chardev stdio,id=con,mux=on -serial chardev:con \
-global virtio-mmio.force-legacy=false \
-device virtio-serial-device,bus=virtio-mmio-bus.0 \
-chardev
socket,telnet=on,host=127.0.0.1,port=3450,server=on,wait=off,id=foo \
-device virtconsole,chardev=foo \
-device virtio-rng-device,bus=virtio-mmio-bus.1 \
-netdev
user,id=u1,hostfwd=tcp:127.0.0.1:10023-10.0.2.15:23,hostfwd=tcp:127.0.0.1:15001-10.0.2.15:5001
\
-device virtio-net-device,netdev=u1,bus=virtio-mmio-bus.2 \
-drive file=./mydisk-1gb.img,if=none,format=raw,id=hd \
-device virtio-blk-device,bus=virtio-mmio-bus.3,drive=hd \
-fsdev
local,security_model=none,id=fsdev0,path=/data/project/code/apache/nuttx \
-device virtio-9p-device,id=fs0,fsdev=fsdev0,mount_tag=host \
-mon chardev=con,mode=readline -kernel
./nuttx/cmake_out/v8a_netnsh/nuttx \
-gdb tcp::7777
[ 0.340000] pci_scan_bus: pci_scan_bus for bus 0
[ 0.340000] pci_scan_bus: class = 00000600, hdr_type = 00000000
[ 0.340000] pci_scan_bus: 00:00 [1b36:0008]
[ 0.350000] pci_setup_device: pbar0 set bad mask
[ 0.350000] pci_setup_device: pbar1 set bad mask
[ 0.350000] pci_setup_device: pbar2 set bad mask
[ 0.350000] pci_setup_device: pbar3 set bad mask
[ 0.350000] pci_setup_device: pbar4 set bad mask
[ 0.350000] pci_setup_device: pbar5 set bad mask
telnetd [4:100]
NuttShell (NSH) NuttX-12.12.0
nsh>
nsh>
nsh> ifconfig
eth0 Link encap:Ethernet HWaddr 00:e0:de:ad:be:ef at RUNNING mtu 1500
inet addr:10.0.2.15 DRaddr:10.0.2.2 Mask:255.255.255.0
IPv4 TCP UDP ICMP
Received 0000 0000 0000 0000
Dropped 0000 0000 0000 0000
IPv4 VHL: 0000 Frg: 0000
Checksum 0000 0000 0000 ----
TCP ACK: 0000 SYN: 0000
RST: 0000 0000
Type 0000 ---- ---- 0000
Sent 0000 0000 0000 0000
Rexmit ---- 0000 ---- ----
nsh> iperf -s -i 1
IP: 10.0.2.15
mode=tcp-server sip=10.0.2.15:5001,dip=0.0.0.0:5001, interval=1, time=0
accept: 10.0.2.2:33612
Interval Transfer Bandwidth
0.00- 1.01 sec 9500924 Bytes 75.25 Mbits/sec
1.01- 2.02 sec 9568256 Bytes 75.79 Mbits/sec
2.02- 3.03 sec 9568256 Bytes 75.79 Mbits/sec
3.03- 4.04 sec 9551872 Bytes 75.66 Mbits/sec
4.04- 5.05 sec 9519104 Bytes 75.40 Mbits/sec
5.05- 6.06 sec 9519104 Bytes 75.40 Mbits/sec
6.06- 7.07 sec 9517480 Bytes 75.39 Mbits/sec
7.07- 8.08 sec 9519104 Bytes 75.40 Mbits/sec
8.08- 9.09 sec 9584640 Bytes 75.92 Mbits/sec
9.09- 10.10 sec 9583980 Bytes 75.91 Mbits/sec
closed by the peer: 10.0.2.2:33612
iperf exit
nsh> uname -a
NuttX 12.12.0 de88cf07345-dirty Jan 31 2026 00:19:08 arm64 qemu-armv8a
nsh>
nsh>
nsh>
```
VirtIO-PCI Test
```c
❯ qemu-system-aarch64 -cpu cortex-a53 -nographic \
-machine virt,virtualization=on,gic-version=3 \
-chardev stdio,id=con,mux=on -serial chardev:con \
-device virtio-rng-pci \
-netdev
user,id=u1,hostfwd=tcp:127.0.0.1:10023-10.0.2.15:23,hostfwd=tcp:127.0.0.1:15001-10.0.2.15:5001
\
-device virtio-net-pci,netdev=u1 \
-mon chardev=con,mode=readline -kernel
./nuttx/cmake_out/v8a_netnsh/nuttx \
-gdb tcp::7777
[ 0.310000] pci_scan_bus: pci_scan_bus for bus 0
[ 0.320000] pci_scan_bus: class = 00000600, hdr_type = 00000000
[ 0.320000] pci_scan_bus: 00:00 [1b36:0008]
[ 0.320000] pci_setup_device: pbar0 set bad mask
[ 0.320000] pci_setup_device: pbar1 set bad mask
[ 0.320000] pci_setup_device: pbar2 set bad mask
[ 0.320000] pci_setup_device: pbar3 set bad mask
[ 0.320000] pci_setup_device: pbar4 set bad mask
[ 0.320000] pci_setup_device: pbar5 set bad mask
[ 0.320000] pci_scan_bus: class = 000000ff, hdr_type = 00000000
[ 0.330000] pci_scan_bus: 00:08 [1af4:1005]
[ 0.330000] pci_setup_device: pbar0: mask64=fffffffe 32bytes
[ 0.330000] pci_setup_device: pbar1: mask64=fffffff0 4096bytes
[ 0.330000] pci_setup_device: pbar2 set bad mask
[ 0.330000] pci_setup_device: pbar3 set bad mask
[ 0.330000] pci_setup_device: pbar4: mask64=fffffffffffffff0 16384bytes
[ 0.330000] pci_scan_bus: class = 00000200, hdr_type = 00000000
[ 0.330000] pci_scan_bus: 00:10 [1af4:1000]
[ 0.330000] pci_setup_device: pbar0: mask64=fffffffe 32bytes
[ 0.330000] pci_setup_device: pbar1: mask64=fffffff0 4096bytes
[ 0.330000] pci_setup_device: pbar2 set bad mask
[ 0.340000] pci_setup_device: pbar3 set bad mask
[ 0.340000] pci_setup_device: pbar4: mask64=fffffffffffffff0 16384bytes
telnetd [4:100]
NuttShell (NSH) NuttX-12.12.0
nsh>
nsh>
nsh>
nsh> iperf -s -i 1
IP: 10.0.2.15
mode=tcp-server sip=10.0.2.15:5001,dip=0.0.0.0:5001, interval=1, time=0
accept: 10.0.2.2:34508
Interval Transfer Bandwidth
0.00- 1.01 sec 1680460 Bytes 13.31 Mbits/sec
1.01- 2.02 sec 1679000 Bytes 13.30 Mbits/sec
2.02- 3.03 sec 1712580 Bytes 13.56 Mbits/sec
3.03- 4.04 sec 1679000 Bytes 13.30 Mbits/sec
4.04- 5.05 sec 1712580 Bytes 13.56 Mbits/sec
5.05- 6.06 sec 1679000 Bytes 13.30 Mbits/sec
6.06- 7.07 sec 1712580 Bytes 13.56 Mbits/sec
7.07- 8.08 sec 1679000 Bytes 13.30 Mbits/sec
8.08- 9.09 sec 1712580 Bytes 13.56 Mbits/sec
9.09- 10.10 sec 1679000 Bytes 13.30 Mbits/sec
10.10- 11.11 sec 1712580 Bytes 13.56 Mbits/sec
11.11- 12.12 sec 1679000 Bytes 13.30 Mbits/sec
12.12- 13.13 sec 1712580 Bytes 13.56 Mbits/sec
closed by the peer: 10.0.2.2:34508
iperf exit
nsh> uname -a
NuttX 12.12.0 de88cf07345-dirty Jan 31 2026 00:19:08 arm64 qemu-armv8a
nsh>
```
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