On 2016-11-01 05:31:56 [+0200], Michael S. Tsirkin wrote:
> > > > > >
> > > > > > > - optionally it has been requested to make synchronize_rcu() behave like
> > > > > > > synchronize_rcu_expedited() on shutdown and kexec().
>
> I was trying to say that the fact net core calls expedited sync
> implies that many people care about boot time.
>
> Should rcu_normal_after_boot override rcu_expedited?
> I'm not sure what happens if you specify both ATM.
I think what you asked for is something like this:
diff --git a/kernel/reboot.c b/kernel/reboot.c
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -283,6 +283,7 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
struct pid_namespace *pid_ns = task_active_pid_ns(current);
char buffer[256];
int ret = 0;
+ bool force_rcu_exp = false;
/* We only trust the superuser with rebooting the system. */
if (!ns_capable(pid_ns->user_ns, CAP_SYS_BOOT))
@@ -311,7 +312,19 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off)
cmd = LINUX_REBOOT_CMD_HALT;
+ switch (cmd) {
+ case LINUX_REBOOT_CMD_RESTART:
+ case LINUX_REBOOT_CMD_HALT:
+ case LINUX_REBOOT_CMD_POWER_OFF:
+ case LINUX_REBOOT_CMD_RESTART2:
+ case LINUX_REBOOT_CMD_KEXEC:
+ force_rcu_exp = true;
+ }
+
mutex_lock(&reboot_mutex);
+ if (force_rcu_exp)
+ rcu_expedite_gp();
+
switch (cmd) {
case LINUX_REBOOT_CMD_RESTART:
kernel_restart(NULL);
@@ -362,6 +375,8 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
ret = -EINVAL;
break;
}
+ if (force_rcu_exp)
+ rcu_unexpedite_gp();
mutex_unlock(&reboot_mutex);
return ret;
}
and problem that this patch is pointless because it is too late. This
RESTART, POWER_OFF, KEXEC hooks here called once the `shutdown' binary
is done doing sync & cleanup and invokes the kernel for the final
operation.
So to achieve what you ask for, we would need a
LINUX_REBOOT_CMD_RCU_FAST option which is invoked by the `shutdown'
binary as the first thing - long before it gets to
LINUX_REBOOT_CMD_RESTART (or KEXEC).
Sebastian
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