hv_exc: Improve multi-core scalability

The HV tick polling now only runs on CPU#0. All CPUs have the 1000Hz
HV tick, but secondaries only use it to poll the FIQ state and that path
does not take the BHL if no other FIQ was pending.

Signed-off-by: Hector Martin <marcan@marcan.st>

src/hv.c

@@ -307,7 +307,12 @@ void hv_rearm(void)
     msr(CNTP_CTL_EL0, CNTx_CTL_ENABLE);
 }
 
-void hv_check_rendezvous(struct exc_info *ctx)
+bool hv_want_rendezvous(void)
+{
+    return hv_want_cpu != -1;
+}
+
+void hv_do_rendezvous(struct exc_info *ctx)
 {
     if (hv_want_cpu == smp_id()) {
         hv_want_cpu = -1;
@@ -323,12 +328,15 @@ void hv_check_rendezvous(struct exc_info *ctx)
     }
 }
 
-void hv_tick(struct exc_info *ctx)
+void hv_maybe_exit(void)
 {
     if (hv_should_exit) {
-        spin_unlock(&bhl);
         hv_exit_guest();
     }
+}
+
+void hv_tick(struct exc_info *ctx)
+{
     hv_wdt_pet();
     iodev_handle_events(uartproxy_iodev);
     if (iodev_can_read(uartproxy_iodev)) {

src/hv.h

@@ -97,7 +97,9 @@ void hv_rendezvous(void);
 void hv_switch_cpu(int cpu);
 void hv_arm_tick(void);
 void hv_rearm(void);
-void hv_check_rendezvous(struct exc_info *ctx);
+bool hv_want_rendezvous(void);
+void hv_do_rendezvous(struct exc_info *ctx);
+void hv_maybe_exit(void);
 void hv_tick(struct exc_info *ctx);
 
 #endif

src/hv_exc.c

@@ -19,15 +19,17 @@ extern spinlock_t bhl;
      ((op2) << ESR_ISS_MSR_OP2_SHIFT))
 #define SYSREG_ISS(...) _SYSREG_ISS(__VA_ARGS__)
 
-#define D_PERCPU(t, x) t x[MAX_CPUS]
-#define PERCPU(x)      x[mrs(TPIDR_EL2)]
+#define PERCPU(x) pcpu[mrs(TPIDR_EL2)].x
 
-D_PERCPU(static bool, ipi_queued);
-D_PERCPU(static bool, ipi_pending);
-D_PERCPU(static bool, pmc_pending);
-D_PERCPU(static u64, pmc_irq_mode);
+struct hv_pcpu_data {
+    u32 ipi_queued;
+    u32 ipi_pending;
+    u32 pmc_pending;
+    u64 pmc_irq_mode;
+    u64 exc_entry_pmcr0_cnt;
+} ALIGNED(64);
 
-D_PERCPU(static u64, exc_entry_pmcr0_cnt);
+struct hv_pcpu_data pcpu[MAX_CPUS];
 
 void hv_exit_guest(void) __attribute__((noreturn));
 
@@ -216,7 +218,7 @@ static bool hv_handle_msr(struct exc_info *ctx, u64 iss)
             msr(SYS_IMP_APL_IPI_RR_LOCAL_EL1, regs[rt]);
             for (int i = 0; i < MAX_CPUS; i++)
                 if (mpidr == smp_get_mpidr(i))
-                    ipi_queued[i] = true;
+                    pcpu[i].ipi_queued = true;
             return true;
         }
         case SYSREG_ISS(SYS_IMP_APL_IPI_RR_GLOBAL_EL1):
@@ -225,7 +227,7 @@ static bool hv_handle_msr(struct exc_info *ctx, u64 iss)
             msr(SYS_IMP_APL_IPI_RR_GLOBAL_EL1, regs[rt]);
             for (int i = 0; i < MAX_CPUS; i++) {
                 if (mpidr == (smp_get_mpidr(i) & 0xffff))
-                    ipi_queued[i] = true;
+                    pcpu[i].ipi_queued = true;
             }
             return true;
         case SYSREG_ISS(SYS_IMP_APL_IPI_SR_EL1):
@@ -366,10 +368,27 @@ void hv_exc_irq(struct exc_info *ctx)
 
 void hv_exc_fiq(struct exc_info *ctx)
 {
-    hv_wdt_breadcrumb('F');
-    hv_exc_entry(ctx);
+    bool tick = false;
+
+    hv_maybe_exit();
+
     if (mrs(CNTP_CTL_EL0) == (CNTx_CTL_ISTATUS | CNTx_CTL_ENABLE)) {
         msr(CNTP_CTL_EL0, CNTx_CTL_ISTATUS | CNTx_CTL_IMASK | CNTx_CTL_ENABLE);
+        tick = true;
+    }
+
+    if (mrs(TPIDR_EL2) != 0 && !(mrs(ISR_EL1) & 0x40) && !hv_want_rendezvous()) {
+        // Secondary CPU and it was just a timer tick (or spurious), so just update FIQs
+        hv_update_fiq();
+        return;
+    }
+
+    // Slow (single threaded) path
+    hv_wdt_breadcrumb('F');
+    hv_exc_entry(ctx);
+
+    // Only poll for HV events in CPU 0
+    if (tick && mrs(TPIDR_EL2) == 0) {
         hv_tick(ctx);
         hv_arm_tick();
     }
@@ -403,7 +422,7 @@ void hv_exc_fiq(struct exc_info *ctx)
         msr(SYS_IMP_APL_IPI_SR_EL1, IPI_SR_PENDING);
         sysop("isb");
     }
-    hv_check_rendezvous(ctx);
+    hv_do_rendezvous(ctx);
 
     // Handles guest timers
     hv_exc_exit(ctx);