| Message ID | 20221128082816.28518-2-kernelfans@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | srcu: shrink the num of srcu_size_state | expand |
>The state SRCU_SIZE_WAIT_CALL is only used in srcu_gp_start_if_needed(). >And it is not needed. Because counter_wrap_check has guarantee that both >srcu_gp_seq_needed and srcu_gp_seq_needed_exp are not far behind >srcu_gp_seq and no false alarm will be raised by the statement in >srcu_gp_start_if_needed() > > ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s) > >As a result, once if SRCU_SIZE_WAIT_BARRIER is seen, the tree snp can be >used immediately, not need to wait for another srcu_gp_end() to update >the srcu_gp_seq_needed and srcu_gp_seq_needed_exp to avoid false alarm. > >Signed-off-by: Pingfan Liu <kernelfans@gmail.com> >Cc: Lai Jiangshan <jiangshanlai@gmail.com> >Cc: "Paul E. McKenney" <paulmck@kernel.org> >Cc: Frederic Weisbecker <frederic@kernel.org> >Cc: Josh Triplett <josh@joshtriplett.org> >Cc: Steven Rostedt <rostedt@goodmis.org> >Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> >Cc: "Zhang, Qiang1" <qiang1.zhang@intel.com> >To: rcu@vger.kernel.org >--- > 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 1c304fec89c0..fe0759d89c2d 100644 >--- a/kernel/rcu/srcutree.c >+++ b/kernel/rcu/srcutree.c >@@ -1092,7 +1092,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, > check_init_srcu_struct(ssp); > idx = srcu_read_lock(ssp); > ss_state = smp_load_acquire(&ssp->srcu_size_state); >- if (ss_state < SRCU_SIZE_WAIT_CALL) >+ if (ss_state < SRCU_SIZE_WAIT_BARRIER) > sdp = per_cpu_ptr(ssp->sda, 0); Hi Pingfan should it be used get_boot_cpu_id() ? Thanks Zqiang > else > sdp = raw_cpu_ptr(ssp->sda); >-- >2.31.1 >
On Mon, Nov 28, 2022 at 08:40:22AM +0000, Zhang, Qiang1 wrote: > >The state SRCU_SIZE_WAIT_CALL is only used in srcu_gp_start_if_needed(). > >And it is not needed. Because counter_wrap_check has guarantee that both > >srcu_gp_seq_needed and srcu_gp_seq_needed_exp are not far behind > >srcu_gp_seq and no false alarm will be raised by the statement in > >srcu_gp_start_if_needed() > > > > ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s) > > > >As a result, once if SRCU_SIZE_WAIT_BARRIER is seen, the tree snp can be > >used immediately, not need to wait for another srcu_gp_end() to update > >the srcu_gp_seq_needed and srcu_gp_seq_needed_exp to avoid false alarm. > > > >Signed-off-by: Pingfan Liu <kernelfans@gmail.com> > >Cc: Lai Jiangshan <jiangshanlai@gmail.com> > >Cc: "Paul E. McKenney" <paulmck@kernel.org> > >Cc: Frederic Weisbecker <frederic@kernel.org> > >Cc: Josh Triplett <josh@joshtriplett.org> > >Cc: Steven Rostedt <rostedt@goodmis.org> > >Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > >Cc: "Zhang, Qiang1" <qiang1.zhang@intel.com> > >To: rcu@vger.kernel.org > >--- > > 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 1c304fec89c0..fe0759d89c2d 100644 > >--- a/kernel/rcu/srcutree.c > >+++ b/kernel/rcu/srcutree.c > >@@ -1092,7 +1092,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, > > check_init_srcu_struct(ssp); > > idx = srcu_read_lock(ssp); > > ss_state = smp_load_acquire(&ssp->srcu_size_state); > >- if (ss_state < SRCU_SIZE_WAIT_CALL) > >+ if (ss_state < SRCU_SIZE_WAIT_BARRIER) > > sdp = per_cpu_ptr(ssp->sda, 0); > > Hi Pingfan > > should it be used get_boot_cpu_id() ? > I am not sure which branch to work on. Thanks, Pingfan > Thanks > Zqiang > > > else > > sdp = raw_cpu_ptr(ssp->sda); > >-- > >2.31.1 > >
On Mon, Nov 28, 2022 at 10:01:08PM +0800, Pingfan Liu wrote: > On Mon, Nov 28, 2022 at 08:40:22AM +0000, Zhang, Qiang1 wrote: > > >The state SRCU_SIZE_WAIT_CALL is only used in srcu_gp_start_if_needed(). > > >And it is not needed. Because counter_wrap_check has guarantee that both > > >srcu_gp_seq_needed and srcu_gp_seq_needed_exp are not far behind > > >srcu_gp_seq and no false alarm will be raised by the statement in > > >srcu_gp_start_if_needed() > > > > > > ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s) > > > > > >As a result, once if SRCU_SIZE_WAIT_BARRIER is seen, the tree snp can be > > >used immediately, not need to wait for another srcu_gp_end() to update > > >the srcu_gp_seq_needed and srcu_gp_seq_needed_exp to avoid false alarm. > > > > > >Signed-off-by: Pingfan Liu <kernelfans@gmail.com> > > >Cc: Lai Jiangshan <jiangshanlai@gmail.com> > > >Cc: "Paul E. McKenney" <paulmck@kernel.org> > > >Cc: Frederic Weisbecker <frederic@kernel.org> > > >Cc: Josh Triplett <josh@joshtriplett.org> > > >Cc: Steven Rostedt <rostedt@goodmis.org> > > >Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > > >Cc: "Zhang, Qiang1" <qiang1.zhang@intel.com> > > >To: rcu@vger.kernel.org > > >--- > > > 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 1c304fec89c0..fe0759d89c2d 100644 > > >--- a/kernel/rcu/srcutree.c > > >+++ b/kernel/rcu/srcutree.c > > >@@ -1092,7 +1092,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, > > > check_init_srcu_struct(ssp); > > > idx = srcu_read_lock(ssp); > > > ss_state = smp_load_acquire(&ssp->srcu_size_state); > > >- if (ss_state < SRCU_SIZE_WAIT_CALL) > > >+ if (ss_state < SRCU_SIZE_WAIT_BARRIER) > > > sdp = per_cpu_ptr(ssp->sda, 0); > > > > Hi Pingfan > > > > should it be used get_boot_cpu_id() ? > > I am not sure which branch to work on. For RCU patches, the "dev" branch of the -rcu tree. For more information, please see: https://mirrors.edge.kernel.org/pub/linux/kernel/people/paulmck/rcutodo.html Thanx, Paul > Thanks, > > Pingfan > > > Thanks > > Zqiang > > > > > else > > > sdp = raw_cpu_ptr(ssp->sda); > > >-- > > >2.31.1 > > >
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 1c304fec89c0..fe0759d89c2d 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1092,7 +1092,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, check_init_srcu_struct(ssp); idx = srcu_read_lock(ssp); ss_state = smp_load_acquire(&ssp->srcu_size_state); - if (ss_state < SRCU_SIZE_WAIT_CALL) + if (ss_state < SRCU_SIZE_WAIT_BARRIER) sdp = per_cpu_ptr(ssp->sda, 0); else sdp = raw_cpu_ptr(ssp->sda);
The state SRCU_SIZE_WAIT_CALL is only used in srcu_gp_start_if_needed(). And it is not needed. Because counter_wrap_check has guarantee that both srcu_gp_seq_needed and srcu_gp_seq_needed_exp are not far behind srcu_gp_seq and no false alarm will be raised by the statement in srcu_gp_start_if_needed() ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s) As a result, once if SRCU_SIZE_WAIT_BARRIER is seen, the tree snp can be used immediately, not need to wait for another srcu_gp_end() to update the srcu_gp_seq_needed and srcu_gp_seq_needed_exp to avoid false alarm. Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: "Zhang, Qiang1" <qiang1.zhang@intel.com> To: rcu@vger.kernel.org --- kernel/rcu/srcutree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)