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fix(igc): do not use num_cpu() when slecting the number of queues #695

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Merged
ytakano merged 2 commits into from
Jun 12, 2026
Merged

fix(igc): do not use num_cpu() when slecting the number of queues #695

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fix(igc): do not use `num_cpu()` when slecting the number of queues
ytakano Jun 12, 2026
8c3419d
add a doc comment regarding the number of CPU
ytakano Jun 12, 2026
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14 changes: 9 additions & 5 deletions awkernel_drivers/src/pcie/intel/igc.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1494,17 +1494,21 @@ fn igc_is_valid_ether_addr(addr: &[u8; 6]) -> bool {

/// Select the number of Rx/Tx queue pairs to enable.
///
/// The result is constrained by three factors:
/// The result is constrained by two factors:
/// 1. **MSI-X vectors**: one vector per queue plus one for link events.
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atsushi421 marked this conversation as resolved.
/// 2. **CPU count**: no benefit in having more queues than CPUs.
/// 3. **Hardware cap**: IGC/I225 supports at most 4 RSS queues.
/// 2. **Hardware cap**: IGC/I225 supports at most 4 RSS queues.
///
/// The result is rounded down to the nearest power of two (1, 2, or 4) so that
/// the 128-entry RSS redirection table divides evenly among queues, giving each
/// queue an equal share of hashed flows.
///
/// Note: for future extensibility
///
/// `num_cpu()` is not available when this function is called during device initialization.
/// If the number of CPU cores is needed to determine the number of queues, the driver should
/// find the number of CPU cores through other means (e.g., ACPI tables).
fn igc_select_num_queues(available_vectors: usize) -> usize {
let cpu_count = core::cmp::max(1, awkernel_lib::cpu::num_cpu());
let available = core::cmp::min(core::cmp::min(available_vectors, cpu_count), 4);
let available = core::cmp::min(available_vectors, 4);

if available >= 4 {
4
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