b/include/linux/srcu.h | 2 b/include/linux/srcutiny.h | 3 b/include/linux/srcutree.h | 38 ---------- b/kernel/rcu/rcutorture.c | 7 - b/kernel/rcu/refscale.c | 32 -------- b/scripts/checkpatch.pl | 2 b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST | 1 include/linux/srcu.h | 47 ------------- tools/testing/selftests/rcutorture/configs/rcu/SRCU-L | 10 -- tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot | 3 10 files changed, 4 insertions(+), 141 deletions(-)
Hello! This series removes the deprecated SRCU-lite flavor: 1. Remove support for SRCU-lite. 2. Remove SRCU-lite scenarios. 3. Remove support for SRCU-lite. 4. Remove SRCU-lite implementation. 5. Remove SRCU-lite deprecation. Thanx, Paul ------------------------------------------------------------------------ b/include/linux/srcu.h | 2 b/include/linux/srcutiny.h | 3 b/include/linux/srcutree.h | 38 ---------- b/kernel/rcu/rcutorture.c | 7 - b/kernel/rcu/refscale.c | 32 -------- b/scripts/checkpatch.pl | 2 b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST | 1 include/linux/srcu.h | 47 ------------- tools/testing/selftests/rcutorture/configs/rcu/SRCU-L | 10 -- tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot | 3 10 files changed, 4 insertions(+), 141 deletions(-)
Hello! This series removes the deprecated SRCU-lite flavor. Both SRCU-lite and SRCU-fast provide faster readers by dropping the smp_mb() call from their lock and unlock primitives. The price of this is a pair of added RCU grace periods during the SRCU grace period. SRCU-fast also adds NMI safety for architectures that have NMIs but do not have NMI-safe per-CPU operations. In addition, srcu_read_lock_fast() returns a per-CPU pointer rather than an integer, which provides a further speedup compared to SRCU-lite by getting rid of array-index calculations. There is a trivial mapping from the SRCU-lite API to that of SRCU-fast, so we do not expect any transition issues. In addition, while SRCU-lite remains in the kernel, checkpatch.pl will warn about added SRCU-lite use cases. Further read-side speedups are possible, but they amount to only about half a nanosecond out of about two nanoseconds (measured on my x86 laptop), and they might require some changes to existing SRCU code. These changes are trivial, but we need to see a solid need for the additional performance before inconveniencing existing users. 1. Remove support for SRCU-lite. 2. Remove SRCU-lite scenarios. 3. Remove support for SRCU-lite. 4. Remove SRCU-lite implementation. 5. Remove SRCU-lite deprecation. Changes since v1: o Add short explanation of SRCU-lite and SRCU-fast. Thanx, Paul ------------------------------------------------------------------------ b/include/linux/srcu.h | 2 b/include/linux/srcutiny.h | 3 b/include/linux/srcutree.h | 38 ---------- b/kernel/rcu/rcutorture.c | 7 - b/kernel/rcu/refscale.c | 32 -------- b/scripts/checkpatch.pl | 2 b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST | 1 include/linux/srcu.h | 47 ------------- tools/testing/selftests/rcutorture/configs/rcu/SRCU-L | 10 -- tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot | 3 10 files changed, 4 insertions(+), 141 deletions(-)
Because SRCU-lite is being replaced by SRCU-fast, this commit removes
support for SRCU-lite from refscale.c.
Both SRCU-lite and SRCU-fast provide faster readers by dropping the
smp_mb() call from their lock and unlock primitives, but incur a pair
of added RCU grace periods during the SRCU grace period. There is a
trivial mapping from the SRCU-lite API to that of SRCU-fast, so there
should be no transition issues.
[ paulmck: Apply Christoph Hellwig feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/refscale.c | 32 +-------------------------------
1 file changed, 1 insertion(+), 31 deletions(-)
diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index f11a7c2af778c..f4b2cea1cce5e 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -246,36 +246,6 @@ static const struct ref_scale_ops srcu_fast_ops = {
.name = "srcu-fast"
};
-static void srcu_lite_ref_scale_read_section(const int nloops)
-{
- int i;
- int idx;
-
- for (i = nloops; i >= 0; i--) {
- idx = srcu_read_lock_lite(srcu_ctlp);
- srcu_read_unlock_lite(srcu_ctlp, idx);
- }
-}
-
-static void srcu_lite_ref_scale_delay_section(const int nloops, const int udl, const int ndl)
-{
- int i;
- int idx;
-
- for (i = nloops; i >= 0; i--) {
- idx = srcu_read_lock_lite(srcu_ctlp);
- un_delay(udl, ndl);
- srcu_read_unlock_lite(srcu_ctlp, idx);
- }
-}
-
-static const struct ref_scale_ops srcu_lite_ops = {
- .init = rcu_sync_scale_init,
- .readsection = srcu_lite_ref_scale_read_section,
- .delaysection = srcu_lite_ref_scale_delay_section,
- .name = "srcu-lite"
-};
-
#ifdef CONFIG_TASKS_RCU
// Definitions for RCU Tasks ref scale testing: Empty read markers.
@@ -1193,7 +1163,7 @@ ref_scale_init(void)
long i;
int firsterr = 0;
static const struct ref_scale_ops *scale_ops[] = {
- &rcu_ops, &srcu_ops, &srcu_fast_ops, &srcu_lite_ops, RCU_TRACE_OPS RCU_TASKS_OPS
+ &rcu_ops, &srcu_ops, &srcu_fast_ops, RCU_TRACE_OPS RCU_TASKS_OPS
&refcnt_ops, &rwlock_ops, &rwsem_ops, &lock_ops, &lock_irq_ops,
&acqrel_ops, &sched_clock_ops, &clock_ops, &jiffies_ops,
&typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops,
--
2.40.1This commit prepares for the removal of SRCU-Lite by removing the SRCU-L
rcutorture scenario that tests it.
Both SRCU-lite and SRCU-fast provide faster readers by dropping the
smp_mb() call from their lock and unlock primitives, but incur a pair
of added RCU grace periods during the SRCU grace period. There is a
trivial mapping from the SRCU-lite API to that of SRCU-fast, so there
should be no transition issues.
[ paulmck: Apply Christoph Hellwig feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
tools/testing/selftests/rcutorture/configs/rcu/CFLIST | 1 -
tools/testing/selftests/rcutorture/configs/rcu/SRCU-L | 10 ----------
.../selftests/rcutorture/configs/rcu/SRCU-L.boot | 3 ---
3 files changed, 14 deletions(-)
delete mode 100644 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L
delete mode 100644 tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/CFLIST b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
index 45f572570a8c3..98b6175e5aa09 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
+++ b/tools/testing/selftests/rcutorture/configs/rcu/CFLIST
@@ -5,7 +5,6 @@ TREE04
TREE05
TREE07
TREE09
-SRCU-L
SRCU-N
SRCU-P
SRCU-T
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L
deleted file mode 100644
index 3b4fa8dbef8a9..0000000000000
--- a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L
+++ /dev/null
@@ -1,10 +0,0 @@
-CONFIG_RCU_TRACE=n
-CONFIG_SMP=y
-CONFIG_NR_CPUS=6
-CONFIG_HOTPLUG_CPU=y
-CONFIG_PREEMPT_NONE=y
-CONFIG_PREEMPT_VOLUNTARY=n
-CONFIG_PREEMPT=n
-#CHECK#CONFIG_RCU_EXPERT=n
-CONFIG_KPROBES=n
-CONFIG_FTRACE=n
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot
deleted file mode 100644
index 0207b3138c5be..0000000000000
--- a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-L.boot
+++ /dev/null
@@ -1,3 +0,0 @@
-rcutorture.torture_type=srcu
-rcutorture.reader_flavor=0x4
-rcutorture.fwd_progress=3
--
2.40.1This commit removes the SRCU-lite implementation, which has been replaced
by SRCU-fast.
Both SRCU-lite and SRCU-fast provide faster readers by dropping the
smp_mb() call from their lock and unlock primitives, but incur a pair
of added RCU grace periods during the SRCU grace period. There is a
trivial mapping from the SRCU-lite API to that of SRCU-fast, so there
should be no transition issues.
[ paulmck: Apply Christoph Hellwig feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
include/linux/srcu.h | 47 ++--------------------------------------
include/linux/srcutiny.h | 3 ---
include/linux/srcutree.h | 38 --------------------------------
3 files changed, 2 insertions(+), 86 deletions(-)
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index c20dacb563e55..cf711a0f440b2 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -46,11 +46,11 @@ int init_srcu_struct(struct srcu_struct *ssp);
/* Values for SRCU Tree srcu_data ->srcu_reader_flavor, but also used by rcutorture. */
#define SRCU_READ_FLAVOR_NORMAL 0x1 // srcu_read_lock().
#define SRCU_READ_FLAVOR_NMI 0x2 // srcu_read_lock_nmisafe().
-#define SRCU_READ_FLAVOR_LITE 0x4 // srcu_read_lock_lite().
+// 0x4 // SRCU-lite is no longer with us.
#define SRCU_READ_FLAVOR_FAST 0x8 // srcu_read_lock_fast().
#define SRCU_READ_FLAVOR_ALL (SRCU_READ_FLAVOR_NORMAL | SRCU_READ_FLAVOR_NMI | \
SRCU_READ_FLAVOR_FAST) // All of the above.
-#define SRCU_READ_FLAVOR_SLOWGP (SRCU_READ_FLAVOR_LITE | SRCU_READ_FLAVOR_FAST)
+#define SRCU_READ_FLAVOR_SLOWGP SRCU_READ_FLAVOR_FAST
// Flavors requiring synchronize_rcu()
// instead of smp_mb().
void __srcu_read_unlock(struct srcu_struct *ssp, int idx) __releases(ssp);
@@ -299,33 +299,6 @@ static inline struct srcu_ctr __percpu *srcu_down_read_fast(struct srcu_struct *
return __srcu_read_lock_fast(ssp);
}
-/**
- * srcu_read_lock_lite - register a new reader for an SRCU-protected structure.
- * @ssp: srcu_struct in which to register the new reader.
- *
- * Enter an SRCU read-side critical section, but for a light-weight
- * smp_mb()-free reader. See srcu_read_lock() for more information.
- *
- * If srcu_read_lock_lite() is ever used on an srcu_struct structure,
- * then none of the other flavors may be used, whether before, during,
- * or after. Note that grace-period auto-expediting is disabled for _lite
- * srcu_struct structures because auto-expedited grace periods invoke
- * synchronize_rcu_expedited(), IPIs and all.
- *
- * Note that srcu_read_lock_lite() can be invoked only from those contexts
- * where RCU is watching, that is, from contexts where it would be legal
- * to invoke rcu_read_lock(). Otherwise, lockdep will complain.
- */
-static inline int srcu_read_lock_lite(struct srcu_struct *ssp) __acquires(ssp)
-{
- int retval;
-
- srcu_check_read_flavor_force(ssp, SRCU_READ_FLAVOR_LITE);
- retval = __srcu_read_lock_lite(ssp);
- rcu_try_lock_acquire(&ssp->dep_map);
- return retval;
-}
-
/**
* srcu_read_lock_nmisafe - register a new reader for an SRCU-protected structure.
* @ssp: srcu_struct in which to register the new reader.
@@ -434,22 +407,6 @@ static inline void srcu_up_read_fast(struct srcu_struct *ssp, struct srcu_ctr __
__srcu_read_unlock_fast(ssp, scp);
}
-/**
- * srcu_read_unlock_lite - unregister a old reader from an SRCU-protected structure.
- * @ssp: srcu_struct in which to unregister the old reader.
- * @idx: return value from corresponding srcu_read_lock_lite().
- *
- * Exit a light-weight SRCU read-side critical section.
- */
-static inline void srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
- __releases(ssp)
-{
- WARN_ON_ONCE(idx & ~0x1);
- srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_LITE);
- srcu_lock_release(&ssp->dep_map);
- __srcu_read_unlock_lite(ssp, idx);
-}
-
/**
* srcu_read_unlock_nmisafe - unregister a old reader from an SRCU-protected structure.
* @ssp: srcu_struct in which to unregister the old reader.
diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 380260317d98b..51ce25f07930e 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -93,9 +93,6 @@ static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_
__srcu_read_unlock(ssp, __srcu_ptr_to_ctr(ssp, scp));
}
-#define __srcu_read_lock_lite __srcu_read_lock
-#define __srcu_read_unlock_lite __srcu_read_unlock
-
static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
{
synchronize_srcu(ssp);
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 8bed7e6cc4c1f..bf44d8d1e69ea 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -278,44 +278,6 @@ static inline void __srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_
RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_fast().");
}
-/*
- * Counts the new reader in the appropriate per-CPU element of the
- * srcu_struct. Returns an index that must be passed to the matching
- * srcu_read_unlock_lite().
- *
- * Note that this_cpu_inc() is an RCU read-side critical section either
- * because it disables interrupts, because it is a single instruction,
- * or because it is a read-modify-write atomic operation, depending on
- * the whims of the architecture.
- */
-static inline int __srcu_read_lock_lite(struct srcu_struct *ssp)
-{
- struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp);
-
- RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_lock_lite().");
- this_cpu_inc(scp->srcu_locks.counter); /* Y */
- barrier(); /* Avoid leaking the critical section. */
- return __srcu_ptr_to_ctr(ssp, scp);
-}
-
-/*
- * Removes the count for the old reader from the appropriate
- * per-CPU element of the srcu_struct. Note that this may well be a
- * different CPU than that which was incremented by the corresponding
- * srcu_read_lock_lite(), but it must be within the same task.
- *
- * Note that this_cpu_inc() is an RCU read-side critical section either
- * because it disables interrupts, because it is a single instruction,
- * or because it is a read-modify-write atomic operation, depending on
- * the whims of the architecture.
- */
-static inline void __srcu_read_unlock_lite(struct srcu_struct *ssp, int idx)
-{
- barrier(); /* Avoid leaking the critical section. */
- this_cpu_inc(__srcu_ctr_to_ptr(ssp, idx)->srcu_unlocks.counter); /* Z */
- RCU_LOCKDEP_WARN(!rcu_is_watching(), "RCU must be watching srcu_read_unlock_lite().");
-}
-
void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
// Record reader usage even for CONFIG_PROVE_RCU=n kernels. This is
--
2.40.1Now that SRCU-lite has been removed from the kernel, let's remove the
now-redundant deprecation from checkpatch.pl.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
scripts/checkpatch.pl | 2 --
1 file changed, 2 deletions(-)
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 664f7b7a622c2..867c7b6fd839f 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -857,8 +857,6 @@ our %deprecated_apis = (
"kunmap" => "kunmap_local",
"kmap_atomic" => "kmap_local_page",
"kunmap_atomic" => "kunmap_local",
- "srcu_read_lock_lite" => "srcu_read_lock_fast",
- "srcu_read_unlock_lite" => "srcu_read_unlock_fast",
);
#Create a search pattern for all these strings to speed up a loop below
--
2.40.1© 2016 - 2025 Red Hat, Inc.