> From: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > Sent: Saturday, February 25, 2023 11:34 AM > To: linux-kernel@xxxxxxxxxxxxxxx > Cc: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>; Frederic Weisbecker > <frederic@xxxxxxxxxx>; Lai Jiangshan <jiangshanlai@xxxxxxxxx>; linux- > doc@xxxxxxxxxxxxxxx; Paul E. McKenney <paulmck@xxxxxxxxxx>; > rcu@xxxxxxxxxxxxxxx > Subject: [PATCH RFC v2] rcu: Add a minimum time for marking boot as > completed > > On many systems, a great deal of boot happens after the kernel thinks the > boot has completed. It is difficult to determine if the system has really > booted from the kernel side. Some features like lazy-RCU can risk slowing > down boot time if, say, a callback has been added that the boot > synchronously depends on. > > Further, it is better to boot systems which pass 'rcu_normal_after_boot' to > stay expedited for as long as the system is still booting. > > For these reasons, this commit adds a config option > 'CONFIG_RCU_BOOT_END_DELAY' and a boot parameter > rcupdate.boot_end_delay. > > By default, this value is 20s. A system designer can choose to specify a value > here to keep RCU from marking boot completion. The boot sequence will not > be marked ended until at least boot_end_delay milliseconds have passed. Hi Joel, Just some thoughts on the default value of 20s, correct me if I'm wrong :-). Does the OS with CONFIG_PREEMPT_RT=y kernel concern more about the real-time latency than the overall OS boot time? If so, we might make rcupdate.boot_end_delay = 0 as the default value (NOT the default 20s) for CONFIG_PREEMPT_RT=y kernels? -Qiuxu > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > --- > v1->v2: > Update some comments and description. > ...
