feat(bench): add queue benches

Add benchmarks for `Queue` and `DesciptorChain` objects.
This will allows us to see performance difference with
changes introduced to the queue in the future.

Signed-off-by: Egor Lazarchuk <[email protected]>

Author: ShadowCurse

src/vmm/Cargo.toml

@@ -61,5 +61,9 @@ tracing = ["log-instrument"]
 name = "cpu_templates"
 harness = false
 
+[[bench]]
+name = "queue"
+harness = false
+
 [lints]
 workspace = true

src/vmm/benches/queue.rs

@@ -0,0 +1,187 @@
+// Copyright 2024 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+//
+// Benchmarking cases:
+//   * `Queue.pop`
+//   * `Queue.add_used`
+//   * `DescriptorChain.next_descriptor`
+
+use std::num::Wrapping;
+
+use criterion::{criterion_group, criterion_main, Criterion};
+use vm_memory::GuestAddress;
+use vmm::devices::virtio::queue::{VIRTQ_DESC_F_NEXT, VIRTQ_DESC_F_WRITE};
+use vmm::devices::virtio::test_utils::VirtQueue;
+use vmm::utilities::test_utils::single_region_mem;
+
+/// Create one chain with n descriptors
+/// Descriptor buffers will leave at the offset of 2048 bytes
+/// to leave some room for queue objects.
+/// We don't really care about sizes of descriptors,
+/// so pick 1024.
+fn set_dtable_one_chain(rxq: &VirtQueue, n: usize) {
+    let desc_size = 1024;
+    for i in 0..n {
+        rxq.dtable[i].set(
+            (2048 + desc_size * i) as u64,
+            desc_size as u32,
+            VIRTQ_DESC_F_WRITE | VIRTQ_DESC_F_NEXT,
+            (i + 1) as u16,
+        );
+    }
+    rxq.dtable[n - 1].flags.set(VIRTQ_DESC_F_WRITE);
+    rxq.dtable[n - 1].next.set(0);
+    rxq.avail.ring[0].set(0);
+    rxq.avail.idx.set(n as u16);
+}
+
+/// Create n chains with 1 descriptors each
+/// Descriptor buffers will leave at the offset of 2048 bytes
+/// to leave some room for queue objects.
+/// We don't really care about sizes of descriptors,
+/// so pick 1024.
+fn set_dtable_many_chains(rxq: &VirtQueue, n: usize) {
+    let desc_size = 1024;
+    for i in 0..n {
+        rxq.dtable[i].set(
+            (2048 + desc_size * i) as u64,
+            desc_size as u32,
+            VIRTQ_DESC_F_WRITE,
+            0,
+        );
+        rxq.avail.ring[i].set(i as u16);
+    }
+    rxq.avail.idx.set(n as u16);
+}
+
+pub fn queue_benchmark(c: &mut Criterion) {
+    let mem = single_region_mem(65562);
+    let rxq = VirtQueue::new(GuestAddress(0), &mem, 256);
+    let mut queue = rxq.create_queue();
+
+    set_dtable_one_chain(&rxq, 1);
+    queue.next_avail = Wrapping(0);
+    let desc = queue.pop(&mem).unwrap();
+    c.bench_function("next_descriptor_1", |b| {
+        b.iter(|| {
+            let mut head = Some(desc.clone());
+            while let Some(d) = head {
+                head = std::hint::black_box(d.next_descriptor());
+            }
+        })
+    });
+
+    set_dtable_one_chain(&rxq, 2);
+    queue.next_avail = Wrapping(0);
+    let desc = queue.pop(&mem).unwrap();
+    c.bench_function("next_descriptor_2", |b| {
+        b.iter(|| {
+            let mut head = Some(desc.clone());
+            while let Some(d) = head {
+                head = std::hint::black_box(d.next_descriptor());
+            }
+        })
+    });
+
+    set_dtable_one_chain(&rxq, 4);
+    queue.next_avail = Wrapping(0);
+    let desc = queue.pop(&mem).unwrap();
+    c.bench_function("next_descriptor_4", |b| {
+        b.iter(|| {
+            let mut head = Some(desc.clone());
+            while let Some(d) = head {
+                head = std::hint::black_box(d.next_descriptor());
+            }
+        })
+    });
+
+    set_dtable_one_chain(&rxq, 16);
+    queue.next_avail = Wrapping(0);
+    let desc = queue.pop(&mem).unwrap();
+    c.bench_function("next_descriptor_16", |b| {
+        b.iter(|| {
+            let mut head = Some(desc.clone());
+            while let Some(d) = head {
+                head = std::hint::black_box(d.next_descriptor());
+            }
+        })
+    });
+
+    // Queue pop
+
+    set_dtable_many_chains(&rxq, 1);
+    c.bench_function("queue_pop_1", |b| {
+        b.iter(|| {
+            queue.next_avail = Wrapping(0);
+            while let Some(desc) = queue.pop(&mem) {
+                std::hint::black_box(desc);
+            }
+        })
+    });
+
+    set_dtable_many_chains(&rxq, 4);
+    c.bench_function("queue_pop_4", |b| {
+        b.iter(|| {
+            queue.next_avail = Wrapping(0);
+            while let Some(desc) = queue.pop(&mem) {
+                std::hint::black_box(desc);
+            }
+        })
+    });
+
+    set_dtable_many_chains(&rxq, 16);
+    c.bench_function("queue_pop_16", |b| {
+        b.iter(|| {
+            queue.next_avail = Wrapping(0);
+            while let Some(desc) = queue.pop(&mem) {
+                std::hint::black_box(desc);
+            }
+        })
+    });
+
+    c.bench_function("queue_add_used_1", |b| {
+        b.iter(|| {
+            queue.num_added = Wrapping(0);
+            queue.next_used = Wrapping(0);
+            for i in 0_u16..1_u16 {
+                let index = std::hint::black_box(i);
+                let len = std::hint::black_box(i + 1);
+                _ = queue.add_used(&mem, index as u16, len as u32);
+            }
+        })
+    });
+
+    c.bench_function("queue_add_used_16", |b| {
+        b.iter(|| {
+            queue.num_added = Wrapping(0);
+            queue.next_used = Wrapping(0);
+            for i in 0_u16..16_u16 {
+                let index = std::hint::black_box(i);
+                let len = std::hint::black_box(i + 1);
+                _ = queue.add_used(&mem, index as u16, len as u32);
+            }
+        })
+    });
+
+    c.bench_function("queue_add_used_256", |b| {
+        b.iter(|| {
+            queue.num_added = Wrapping(0);
+            queue.next_used = Wrapping(0);
+            for i in 0_u16..256_u16 {
+                let index = std::hint::black_box(i);
+                let len = std::hint::black_box(i + 1);
+                _ = queue.add_used(&mem, index as u16, len as u32);
+            }
+        })
+    });
+}
+
+criterion_group! {
+    name = queue_benches;
+    config = Criterion::default().sample_size(200).noise_threshold(0.05);
+    targets = queue_benchmark
+}
+
+criterion_main! {
+    queue_benches
+}

src/vmm/src/devices/virtio/queue.rs

@@ -16,8 +16,8 @@ use crate::vstate::memory::{
     Address, ByteValued, Bytes, GuestAddress, GuestMemory, GuestMemoryMmap,
 };
 
-pub(super) const VIRTQ_DESC_F_NEXT: u16 = 0x1;
-pub(super) const VIRTQ_DESC_F_WRITE: u16 = 0x2;
+pub const VIRTQ_DESC_F_NEXT: u16 = 0x1;
+pub const VIRTQ_DESC_F_WRITE: u16 = 0x2;
 
 /// Max size of virtio queues offered by firecracker's virtio devices.
 pub(super) const FIRECRACKER_MAX_QUEUE_SIZE: u16 = 256;
@@ -69,7 +69,7 @@ struct UsedElement {
 unsafe impl ByteValued for UsedElement {}
 
 /// A virtio descriptor chain.
-#[derive(Debug)]
+#[derive(Debug, Copy, Clone)]
 pub struct DescriptorChain<'a, M: GuestMemory = GuestMemoryMmap> {
     desc_table: GuestAddress,
     queue_size: u16,
@@ -205,7 +205,7 @@ impl<'a> Iterator for DescriptorIterator<'a> {
 /// A virtio queue's parameters.
 pub struct Queue {
     /// The maximal size in elements offered by the device
-    pub(crate) max_size: u16,
+    pub max_size: u16,
 
     /// The queue size in elements the driver selected
     pub size: u16,
@@ -222,13 +222,13 @@ pub struct Queue {
     /// Guest physical address of the used ring
     pub used_ring: GuestAddress,
 
-    pub(crate) next_avail: Wrapping<u16>,
-    pub(crate) next_used: Wrapping<u16>,
+    pub next_avail: Wrapping<u16>,
+    pub next_used: Wrapping<u16>,
 
     /// VIRTIO_F_RING_EVENT_IDX negotiated (notification suppression enabled)
-    pub(crate) uses_notif_suppression: bool,
+    pub uses_notif_suppression: bool,
     /// The number of added used buffers since last guest kick
-    pub(crate) num_added: Wrapping<u16>,
+    pub num_added: Wrapping<u16>,
 }
 
 #[allow(clippy::len_without_is_empty)]