Drivers: hv: vmbus: Optimize boot time by concurrent execution of hv_synic_init()

Currently on a very large system with 1780 CPUs, hv_acpi_init() takes
around 3 seconds to complete. This is because of sequential synic
initialization for each CPU performed by hv_synic_init().

Schedule these tasks parallelly so that each CPU executes hv_synic_init()
in parallel to take full advantage of multiple CPUs.

This solution saves around 2 seconds of boot time on a 1780 CPU system,
which is around 66% improvement in the existing logic.

Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Reviewed-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Srivatsa S. Bhat (Microsoft) <srivatsa@csail.mit.edu>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Link: https://lore.kernel.org/r/1722488136-6223-1-git-send-email-ssengar@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <1722488136-6223-1-git-send-email-ssengar@linux.microsoft.com>

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index c857dc3975be77ab003972f49edfcbbcc77672cc..7242c49204271628e39da5e54cd06a188bbde244 100644 (file)
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1306,6 +1306,13 @@ static irqreturn_t vmbus_percpu_isr(int irq, void *dev_id)
        return IRQ_HANDLED;
 }
 
+static void vmbus_percpu_work(struct work_struct *work)
+{
+       unsigned int cpu = smp_processor_id();
+
+       hv_synic_init(cpu);
+}
+
 /*
  * vmbus_bus_init -Main vmbus driver initialization routine.
  *
@@ -1316,7 +1323,8 @@ static irqreturn_t vmbus_percpu_isr(int irq, void *dev_id)
  */
 static int vmbus_bus_init(void)
 {
-       int ret;
+       int ret, cpu;
+       struct work_struct __percpu *works;
 
        ret = hv_init();
        if (ret != 0) {
@@ -1355,12 +1363,32 @@ static int vmbus_bus_init(void)
        if (ret)
                goto err_alloc;
 
+       works = alloc_percpu(struct work_struct);
+       if (!works) {
+               ret = -ENOMEM;
+               goto err_alloc;
+       }
+
        /*
         * Initialize the per-cpu interrupt state and stimer state.
         * Then connect to the host.
         */
-       ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "hyperv/vmbus:online",
-                               hv_synic_init, hv_synic_cleanup);
+       cpus_read_lock();
+       for_each_online_cpu(cpu) {
+               struct work_struct *work = per_cpu_ptr(works, cpu);
+
+               INIT_WORK(work, vmbus_percpu_work);
+               schedule_work_on(cpu, work);
+       }
+
+       for_each_online_cpu(cpu)
+               flush_work(per_cpu_ptr(works, cpu));
+
+       /* Register the callbacks for possible CPU online/offline'ing */
+       ret = cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ONLINE_DYN, "hyperv/vmbus:online",
+                                                  hv_synic_init, hv_synic_cleanup);
+       cpus_read_unlock();
+       free_percpu(works);
        if (ret < 0)
                goto err_alloc;
        hyperv_cpuhp_online = ret;