| Message ID | 20230704070809.31951-1-qiang.zhang1211@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | srcu: Priority check rcu_gp_is_expedited() in synchronize_srcu() | expand |
On Tue, Jul 04, 2023 at 03:08:09PM +0800, Zqiang wrote: > Since the atomic variable rcu_expedited_nesting is initialized to > true, so the rcu_gp_is_expedited() is always return true during > system startup until the rcu_end_inkernel_boot() is called. this > means that without setting rcupdate.rcu_normal=1 and before the > rcu_end_inkernel_boot() is executed, regardless of whether the > return value of srcu_might_be_idle() is true, call synchronize_srcu() > always fall back to synchronize_srcu_expedited(), so there is > no need to checking srcu_might_be_idle() return value. > > For the rcupdate.rcu_normal=0, rcupdate.rcu_normal_after_boot=0 and > rcupdate.rcu_expedited=1 kernels, there is also no need to checking > srcu_might_be_idle() return value. > > This commit therefore priority check rcu_gp_is_expedited() return value > in synchronize_srcu(). > > Signed-off-by: Zqiang <qiang.zhang1211@gmail.com> Thank you for taking the time to look into SRCU! But are you seeing real performance issues that this addresses? My guess is "no", given that this is nowhere near a fastpath, but I figured that I should ask. Thanx, Paul > --- > kernel/rcu/srcutree.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > index 20d7a238d675..a819f11d9b90 100644 > --- a/kernel/rcu/srcutree.c > +++ b/kernel/rcu/srcutree.c > @@ -1435,7 +1435,7 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited); > */ > void synchronize_srcu(struct srcu_struct *ssp) > { > - if (srcu_might_be_idle(ssp) || rcu_gp_is_expedited()) > + if (rcu_gp_is_expedited() || srcu_might_be_idle(ssp)) > synchronize_srcu_expedited(ssp); > else > __synchronize_srcu(ssp, true); > -- > 2.17.1 >
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 20d7a238d675..a819f11d9b90 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1435,7 +1435,7 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited); */ void synchronize_srcu(struct srcu_struct *ssp) { - if (srcu_might_be_idle(ssp) || rcu_gp_is_expedited()) + if (rcu_gp_is_expedited() || srcu_might_be_idle(ssp)) synchronize_srcu_expedited(ssp); else __synchronize_srcu(ssp, true);
Since the atomic variable rcu_expedited_nesting is initialized to true, so the rcu_gp_is_expedited() is always return true during system startup until the rcu_end_inkernel_boot() is called. this means that without setting rcupdate.rcu_normal=1 and before the rcu_end_inkernel_boot() is executed, regardless of whether the return value of srcu_might_be_idle() is true, call synchronize_srcu() always fall back to synchronize_srcu_expedited(), so there is no need to checking srcu_might_be_idle() return value. For the rcupdate.rcu_normal=0, rcupdate.rcu_normal_after_boot=0 and rcupdate.rcu_expedited=1 kernels, there is also no need to checking srcu_might_be_idle() return value. This commit therefore priority check rcu_gp_is_expedited() return value in synchronize_srcu(). Signed-off-by: Zqiang <qiang.zhang1211@gmail.com> --- kernel/rcu/srcutree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)