vcpu: boost vcpu threads

Add an option to allow boosting vcpu threads with high uclamp so that
it'll move to bigger CPUs and higher frequencies.

BUG=b:342349882
TEST=tools/presubmit
Change-Id: Ib1cb15b0f862acf8ec95a00d12e7de23e0ddcb4f
Signed-off-by: David Dai <davidai@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/5627833
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>

src/crosvm/cmdline.rs

@@ -1043,6 +1043,14 @@ pub struct RunCommand {
     ///     pci-address=ADDR - Preferred PCI address, e.g. "00:01.0".
     block: Vec<DiskOptionWithId>,
 
+    #[cfg(any(target_os = "android", target_os = "linux"))]
+    #[argh(switch)]
+    #[serde(skip)]
+    #[merge(strategy = overwrite_option)]
+    /// set a minimum utilization for vCPU threads which will hint to the host scheduler
+    /// to ramp up higher frequencies or place vCPU threads on larger cores.
+    pub boost_uclamp: Option<bool>,
+
     #[cfg(target_arch = "x86_64")]
     #[argh(switch)]
     #[merge(strategy = overwrite_option)]
@@ -2725,6 +2733,7 @@ impl TryFrom<RunCommand> for super::config::Config {
         #[cfg(any(target_os = "android", target_os = "linux"))]
         {
             cfg.lock_guest_memory = cmd.lock_guest_memory.unwrap_or_default();
+            cfg.boost_uclamp = cmd.boost_uclamp.unwrap_or_default();
         }
 
         #[cfg(feature = "audio")]

src/crosvm/config.rs

@@ -697,6 +697,8 @@ pub struct Config {
     pub block_control_tube: Vec<Tube>,
     #[cfg(windows)]
     pub block_vhost_user_tube: Vec<Tube>,
+    #[cfg(any(target_os = "android", target_os = "linux"))]
+    pub boost_uclamp: bool,
     pub boot_cpu: usize,
     #[cfg(target_arch = "x86_64")]
     pub break_linux_pci_config_io: bool,
@@ -986,6 +988,8 @@ impl Default for Config {
             log_file: None,
             #[cfg(windows)]
             logs_directory: None,
+            #[cfg(any(target_os = "android", target_os = "linux"))]
+            boost_uclamp: false,
             memory: None,
             memory_file: None,
             mmio_address_ranges: Vec::new(),

src/crosvm/sys/linux.rs

@@ -3575,6 +3575,7 @@ fn run_control<V: VmArch + 'static, Vcpu: VcpuArch + 'static>(
             #[cfg(target_arch = "x86_64")]
             bus_lock_ratelimit_ctrl,
             run_mode,
+            cfg.boost_uclamp,
         )?;
         vcpu_handles.push((handle, to_vcpu_channel));
     }

src/crosvm/sys/linux/vcpu.rs

@@ -24,6 +24,8 @@ use arch::LinuxArch;
 use arch::VcpuArch;
 use arch::VcpuInitArch;
 use arch::VmArch;
+use base::sched_attr;
+use base::sched_setattr;
 use base::signal::clear_signal_handler;
 use base::signal::BlockedSignal;
 use base::*;
@@ -35,6 +37,8 @@ use hypervisor::IoParams;
 use hypervisor::VcpuExit;
 use hypervisor::VcpuSignalHandle;
 use libc::c_int;
+use libc::SCHED_FLAG_KEEP_ALL;
+use libc::SCHED_FLAG_RESET_ON_FORK;
 use metrics_events::MetricEventType;
 #[cfg(target_arch = "riscv64")]
 use riscv64::Riscv64 as Arch;
@@ -50,6 +54,10 @@ use super::ExitState;
 #[cfg(target_arch = "x86_64")]
 use crate::crosvm::ratelimit::Ratelimit;
 
+// TODO(davidai): Import libc constant when updated
+const SCHED_FLAG_UTIL_CLAMP_MIN: u64 = 0x20;
+const SCHED_SCALE_CAPACITY: u32 = 1024;
+
 fn bus_io_handler(bus: &Bus) -> impl FnMut(IoParams) -> Option<[u8; 8]> + '_ {
     |IoParams {
          address,
@@ -87,6 +95,7 @@ pub fn set_vcpu_thread_scheduling(
     enable_per_vm_core_scheduling: bool,
     vcpu_cgroup_tasks_file: Option<File>,
     run_rt: bool,
+    boost_uclamp: bool,
 ) -> anyhow::Result<()> {
     if !vcpu_affinity.is_empty() {
         if let Err(e) = set_cpu_affinity(vcpu_affinity) {
@@ -94,6 +103,18 @@ pub fn set_vcpu_thread_scheduling(
         }
     }
 
+    if boost_uclamp {
+        let mut sched_attr = sched_attr::default();
+        sched_attr.sched_flags = SCHED_FLAG_KEEP_ALL as u64
+            | SCHED_FLAG_UTIL_CLAMP_MIN
+            | SCHED_FLAG_RESET_ON_FORK as u64;
+        sched_attr.sched_util_min = SCHED_SCALE_CAPACITY;
+
+        if let Err(e) = sched_setattr(0, &mut sched_attr, 0) {
+            warn!("Failed to boost vcpu util: {}", e);
+        }
+    }
+
     if core_scheduling && !enable_per_vm_core_scheduling {
         // Do per-vCPU core scheduling by setting a unique cookie to each vCPU.
         if let Err(e) = enable_core_scheduling() {
@@ -499,6 +520,7 @@ pub fn run_vcpu<V>(
     vcpu_cgroup_tasks_file: Option<File>,
     #[cfg(target_arch = "x86_64")] bus_lock_ratelimit_ctrl: Arc<Mutex<Ratelimit>>,
     run_mode: VmRunMode,
+    boost_uclamp: bool,
 ) -> Result<JoinHandle<()>>
 where
     V: VcpuArch + 'static,
@@ -516,6 +538,7 @@ where
                     enable_per_vm_core_scheduling,
                     vcpu_cgroup_tasks_file,
                     run_rt && !delay_rt,
+                    boost_uclamp,
                 ) {
                     error!("vcpu thread setup failed: {:#}", e);
                     return ExitState::Stop;