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WIP: a usable CQ completion channel #83

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967871f
WIP: a usable CQ completion channel
dragonJACson Nov 30, 2025
a2fa883
feat(examples): adapt CQ events for rc_pingpong
dragonJACson Nov 30, 2025
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1 change: 1 addition & 0 deletions .cirrus.yml
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,7 @@ task:
- export LD_LIBRARY_PATH=./rdma-core/build/lib
- just test-basic-with-cov
- just test-rc-pingpong-with-cov
- just test-rc-pingpong-with-events-with-cov
- just test-cmtime-with-cov
- just generate-cov
- sed -i 's#/tmp/cirrus-ci-build/##g' lcov.info
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5 changes: 5 additions & 0 deletions Justfile
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,11 @@ test-rc-pingpong-with-cov:
sleep 2
cargo llvm-cov --no-report run --example rc_pingpong_split -- -d {{rdma_dev}} -g 1 127.0.0.1

test-rc-pingpong-with-events-with-cov:
cargo llvm-cov --no-report run --example rc_pingpong_split -- -d {{rdma_dev}} -g 1 -e &
sleep 2
cargo llvm-cov --no-report run --example rc_pingpong_split -- -d {{rdma_dev}} -g 1 -e 127.0.0.1

test-cmtime-with-cov:
cargo llvm-cov --no-report run --example cmtime -- -b {{ip}} &
sleep 2
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210 changes: 126 additions & 84 deletions examples/rc_pingpong.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,8 @@ use postcard::{from_bytes, to_allocvec};
use serde::{Deserialize, Serialize};
use sideway::ibverbs::address::{AddressHandleAttribute, Gid};
use sideway::ibverbs::completion::{
CreateCompletionQueueWorkCompletionFlags, GenericCompletionQueue, WorkCompletionStatus,
CompletionChannel, CreateCompletionQueueWorkCompletionFlags, GenericCompletionQueue, PollCompletionQueueError,
WorkCompletionStatus,
};
use sideway::ibverbs::device::{DeviceInfo, DeviceList};
use sideway::ibverbs::device_context::Mtu;
Expand Down Expand Up @@ -69,6 +70,9 @@ pub struct Args {
/// Get CQE with timestamp
#[arg(long, short = 't', default_value_t = false)]
ts: bool,
/// Use CQ events instead of busy polling
#[arg(long, short = 'e', default_value_t = false)]
use_events: bool,
/// If no value provided, start a server and wait for connection, otherwise, connect to server at [host]
#[arg(name = "host")]
server_ip: Option<String>,
Expand Down Expand Up @@ -156,6 +160,13 @@ fn main() -> anyhow::Result<()> {
}
}

// Create completion channel if using events
let comp_channel = if args.use_events {
Some(CompletionChannel::new(&context).expect("Couldn't create completion channel"))
} else {
None
};

let pd = context.alloc_pd().unwrap_or_else(|_| panic!("Couldn't allocate PD"));
let send_data: Vec<u8> = vec![0; args.size as _];
let send_mr = unsafe {
Expand Down Expand Up @@ -189,16 +200,28 @@ fn main() -> anyhow::Result<()> {
);
}

// Associate completion channel with CQ if using events
if let Some(ref channel) = comp_channel {
cq_builder.setup_comp_channel(channel, 0);
}

let cq = cq_builder.setup_cqe(rx_depth + 1).build_ex().unwrap();

let cq_handle = GenericCompletionQueue::from(Arc::clone(&cq));

// Request initial notification if using events
if args.use_events {
cq_handle
.req_notify_cq(false)
.expect("Couldn't request CQ notification");
}

let mut builder = pd.create_qp_builder();

let mut qp = builder
.setup_max_inline_data(128)
.setup_send_cq(cq_handle.clone())
.setup_recv_cq(cq_handle)
.setup_recv_cq(cq_handle.clone())
.setup_max_send_wr(1)
.setup_max_recv_wr(rx_depth)
.build_ex()
Expand Down Expand Up @@ -324,100 +347,119 @@ fn main() -> anyhow::Result<()> {
outstanding_send = true;
}
// poll for the completion
{
loop {
match cq.start_poll() {
Ok(mut poller) => {
while let Some(wc) = poller.next() {
if wc.status() != WorkCompletionStatus::Success as u32 {
panic!(
"Failed status {:#?} ({}) for wr_id {}",
Into::<WorkCompletionStatus>::into(wc.status()),
wc.status(),
wc.wr_id()
);
}
match wc.wr_id() {
SEND_WR_ID => {
scnt += 1;
outstanding_send = false;
},
RECV_WR_ID => {
rcnt += 1;
rout -= 1;

// Post more receives if the receive side credit is low
if rout <= rx_depth / 2 {
let to_post = rx_depth - rout;
for _ in 0..to_post {
let mut guard = qp.start_post_recv();
let recv_handle = guard.construct_wr(RECV_WR_ID);
unsafe {
recv_handle.setup_sge(
recv_mr.lkey(),
recv_data.as_mut_ptr() as _,
args.size,
);
};
guard.post().unwrap();
}
rout += to_post;
let mut num_cq_events: u32 = 0;
loop {
// If using events, wait for CQ event before polling
if args.use_events {
if let Some(ref channel) = comp_channel {
// Get the CQ event (this blocks until an event arrives)
let _event_cq = channel.get_cq_event().expect("Failed to get CQ event");
num_cq_events += 1;

// Re-arm the notification BEFORE polling to avoid missing events
cq_handle
.req_notify_cq(false)
.expect("Couldn't request CQ notification");
}
}

// Poll for completions
match cq.start_poll() {
Ok(mut poller) => {
while let Some(wc) = poller.next() {
if wc.status() != WorkCompletionStatus::Success as u32 {
panic!(
"Failed status {:#?} ({}) for wr_id {}",
Into::<WorkCompletionStatus>::into(wc.status()),
wc.status(),
wc.wr_id()
);
}
match wc.wr_id() {
SEND_WR_ID => {
scnt += 1;
outstanding_send = false;
},
RECV_WR_ID => {
rcnt += 1;
rout -= 1;

// Post more receives if the receive side credit is low
if rout <= rx_depth / 2 {
let to_post = rx_depth - rout;
for _ in 0..to_post {
let mut guard = qp.start_post_recv();
let recv_handle = guard.construct_wr(RECV_WR_ID);
unsafe {
recv_handle.setup_sge(recv_mr.lkey(), recv_data.as_mut_ptr() as _, args.size);
};
guard.post().unwrap();
}
rout += to_post;
}

if args.ts {
let timestamp = wc.completion_timestamp();
if ts_param.last_completion_with_timestamp != 0 {
let delta: u64 = if timestamp >= ts_param.completion_recv_prev_time {
timestamp - ts_param.completion_recv_prev_time
} else {
completion_timestamp_mask - ts_param.completion_recv_prev_time
+ timestamp
+ 1
};

ts_param.completion_recv_max_time_delta =
ts_param.completion_recv_max_time_delta.max(delta);
ts_param.completion_recv_min_time_delta =
ts_param.completion_recv_min_time_delta.min(delta);
ts_param.completion_recv_total_time_delta += delta;
ts_param.completion_with_time_iters += 1;
}

ts_param.completion_recv_prev_time = timestamp;
ts_param.last_completion_with_timestamp = 1;
} else {
ts_param.last_completion_with_timestamp = 0;
if args.ts {
let timestamp = wc.completion_timestamp();
if ts_param.last_completion_with_timestamp != 0 {
let delta: u64 = if timestamp >= ts_param.completion_recv_prev_time {
timestamp - ts_param.completion_recv_prev_time
} else {
completion_timestamp_mask - ts_param.completion_recv_prev_time + timestamp + 1
};

ts_param.completion_recv_max_time_delta =
ts_param.completion_recv_max_time_delta.max(delta);
ts_param.completion_recv_min_time_delta =
ts_param.completion_recv_min_time_delta.min(delta);
ts_param.completion_recv_total_time_delta += delta;
ts_param.completion_with_time_iters += 1;
}
},
_ => {
panic!("Unknown error!");
},
}

if scnt < args.iter && !outstanding_send {
// Post another send if we haven't reached the iteration limit
let mut guard = qp.start_post_send();
let send_handle = guard.construct_wr(SEND_WR_ID, WorkRequestFlags::Signaled).setup_send();
unsafe {
send_handle.setup_sge(send_mr.lkey(), send_data.as_ptr() as _, args.size);
ts_param.completion_recv_prev_time = timestamp;
ts_param.last_completion_with_timestamp = 1;
} else {
ts_param.last_completion_with_timestamp = 0;
}
guard.post()?;
outstanding_send = true;
},
_ => {
panic!("Unknown error!");
},
}

if scnt < args.iter && !outstanding_send {
// Post another send if we haven't reached the iteration limit
let mut guard = qp.start_post_send();
let send_handle = guard.construct_wr(SEND_WR_ID, WorkRequestFlags::Signaled).setup_send();
unsafe {
send_handle.setup_sge(send_mr.lkey(), send_data.as_ptr() as _, args.size);
}
guard.post()?;
outstanding_send = true;
}
},
Err(_) => {
}
},
Err(PollCompletionQueueError::CompletionQueueEmpty) => {
// CQ is empty - if not using events, continue busy polling
if !args.use_events {
continue;
},
}
}
},
Err(e) => {
panic!("Failed to poll CQ: {:?}", e);
},
}

// Check if we're done
if scnt >= args.iter && rcnt >= args.iter {
break;
}
// Check if we're done
if scnt >= args.iter && rcnt >= args.iter {
break;
}
}

// Acknowledge all CQ events before cleanup
if num_cq_events > 0 {
cq_handle.ack_events(num_cq_events);
}

let end_time = clock.now();
let time = end_time.duration_since(start_time);
let bytes = args.size as u64 * args.iter as u64 * 2;
Expand Down
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