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net_util: queue_pair: Simplify and fix the TX rate limiter

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The TX rate limiter didn't correctly handle the `-EAGAIN` situation
where it should replenish the rate-limiter tokens. This patch simplifies
the TX rate-limiter code path by following the similar trade-off made in
the TX rate limiter, where we always let the `last` descriptor
go-through (even if it was over the rate limit. We simply stop
processing the oncoming `descriptors` if any.

Fixes: #2817

Signed-off-by: Bo Chen <chen.bo@intel.com>
This commit is contained in:
Bo Chen 2021-06-30 16:34:13 -07:00 committed by Rob Bradford
parent 43f1a32859
commit 97b3c9b7b6
1 changed files with 20 additions and 25 deletions
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45
net_util/src/queue_pair.rs
View File

@ -41,33 +41,16 @@ impl TxVirtio {
rate_limiter: &mut Option<RateLimiter>,
) -> Result<bool, NetQueuePairError> {
let mut retry_write = false;
let mut rate_limit_reached = false;
while let Some(avail_desc) = queue.iter(mem).next() {
if rate_limit_reached {
queue.go_to_previous_position();
break;
}
let head_index = avail_desc.index;
let mut next_desc = Some(avail_desc);
if let Some(rate_limiter) = rate_limiter {
if !rate_limiter.consume(1, TokenType::Ops) {
queue.go_to_previous_position();
break;
}
let mut bytes = Wrapping(0);
let mut tmp_next_desc = next_desc.clone();
while let Some(desc) = tmp_next_desc {
if !desc.is_write_only() {
bytes += Wrapping(desc.len as u64);
}
tmp_next_desc = desc.next_descriptor();
}
bytes -= Wrapping(vnet_hdr_len() as u64);
if !rate_limiter.consume(bytes.0, TokenType::Bytes) {
// Revert the OPS consume().
rate_limiter.manual_replenish(1, TokenType::Ops);
queue.go_to_previous_position();
break;
}
}
let mut iovecs = Vec::new();
while let Some(desc) = next_desc {
if !desc.is_write_only() && desc.len > 0 {
@ -84,7 +67,7 @@ impl TxVirtio {
next_desc = desc.next_descriptor();
}
if !iovecs.is_empty() {
let len = if !iovecs.is_empty() {
let result = unsafe {
libc::writev(
tap.as_raw_fd() as libc::c_int,
@ -108,10 +91,22 @@ impl TxVirtio {
self.counter_bytes += Wrapping(result as u64 - vnet_hdr_len() as u64);
self.counter_frames += Wrapping(1);
}
result as u32
} else {
0
};
queue.add_used(mem, head_index, 0);
queue.update_avail_event(mem);
// For the sake of simplicity (similar to the RX rate limiting), we always
// let the 'last' descriptor chain go-through even if it was over the rate
// limit, and simply stop processing oncoming `avail_desc` if any.
if let Some(rate_limiter) = rate_limiter {
rate_limit_reached = !rate_limiter.consume(1, TokenType::Ops)
|| !rate_limiter.consume(len as u64, TokenType::Bytes);
}
}
Ok(retry_write)