* [PATCH tip/core/rcu 2/6] rcu: Convert rcutree_plugin.h printk calls
2013-05-20 14:28 ` [PATCH tip/core/rcu 1/6] rcu: Convert rcutree.c printk calls Paul E. McKenney
@ 2013-05-20 14:28 ` Paul E. McKenney
2013-05-20 14:28 ` [PATCH tip/core/rcu 3/6] rcu: Remove "Experimental" flags Paul E. McKenney
` (3 subsequent siblings)
4 siblings, 0 replies; 7+ messages in thread
From: Paul E. McKenney @ 2013-05-20 14:28 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, laijs, dipankar, akpm, mathieu.desnoyers, josh, niv, tglx,
peterz, rostedt, Valdis.Kletnieks, dhowells, edumazet, darren,
fweisbec, sbw, Paul E. McKenney
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
This commit converts printk() calls to the corresponding pr_*() calls.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
kernel/rcutree_plugin.h | 45 ++++++++++++++++++++++-----------------------
1 file changed, 22 insertions(+), 23 deletions(-)
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 3db5a37..207844e 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -53,38 +53,37 @@ static char __initdata nocb_buf[NR_CPUS * 5];
static void __init rcu_bootup_announce_oddness(void)
{
#ifdef CONFIG_RCU_TRACE
- printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
+ pr_info("\tRCU debugfs-based tracing is enabled.\n");
#endif
#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
- printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
+ pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
CONFIG_RCU_FANOUT);
#endif
#ifdef CONFIG_RCU_FANOUT_EXACT
- printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
+ pr_info("\tHierarchical RCU autobalancing is disabled.\n");
#endif
#ifdef CONFIG_RCU_FAST_NO_HZ
- printk(KERN_INFO
- "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
+ pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
#endif
#ifdef CONFIG_PROVE_RCU
- printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
+ pr_info("\tRCU lockdep checking is enabled.\n");
#endif
#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
- printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
+ pr_info("\tRCU torture testing starts during boot.\n");
#endif
#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
- printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
+ pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
#endif
#if defined(CONFIG_RCU_CPU_STALL_INFO)
- printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
+ pr_info("\tAdditional per-CPU info printed with stalls.\n");
#endif
#if NUM_RCU_LVL_4 != 0
- printk(KERN_INFO "\tFour-level hierarchy is enabled.\n");
+ pr_info("\tFour-level hierarchy is enabled.\n");
#endif
if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
- printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
+ pr_info("\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
if (nr_cpu_ids != NR_CPUS)
- printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
+ pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
#ifdef CONFIG_RCU_NOCB_CPU
#ifndef CONFIG_RCU_NOCB_CPU_NONE
if (!have_rcu_nocb_mask) {
@@ -123,7 +122,7 @@ static int rcu_preempted_readers_exp(struct rcu_node *rnp);
*/
static void __init rcu_bootup_announce(void)
{
- printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
+ pr_info("Preemptible hierarchical RCU implementation.\n");
rcu_bootup_announce_oddness();
}
@@ -490,13 +489,13 @@ static void rcu_print_detail_task_stall(struct rcu_state *rsp)
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
{
- printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
+ pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
rnp->level, rnp->grplo, rnp->grphi);
}
static void rcu_print_task_stall_end(void)
{
- printk(KERN_CONT "\n");
+ pr_cont("\n");
}
#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
@@ -526,7 +525,7 @@ static int rcu_print_task_stall(struct rcu_node *rnp)
t = list_entry(rnp->gp_tasks,
struct task_struct, rcu_node_entry);
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
- printk(KERN_CONT " P%d", t->pid);
+ pr_cont(" P%d", t->pid);
ndetected++;
}
rcu_print_task_stall_end();
@@ -942,7 +941,7 @@ static struct rcu_state *rcu_state = &rcu_sched_state;
*/
static void __init rcu_bootup_announce(void)
{
- printk(KERN_INFO "Hierarchical RCU implementation.\n");
+ pr_info("Hierarchical RCU implementation.\n");
rcu_bootup_announce_oddness();
}
@@ -1883,7 +1882,7 @@ static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
/* Initiate the stall-info list. */
static void print_cpu_stall_info_begin(void)
{
- printk(KERN_CONT "\n");
+ pr_cont("\n");
}
/*
@@ -1914,7 +1913,7 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
ticks_value = rsp->gpnum - rdp->gpnum;
}
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
- printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
+ pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
cpu, ticks_value, ticks_title,
atomic_read(&rdtp->dynticks) & 0xfff,
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
@@ -1925,7 +1924,7 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
/* Terminate the stall-info list. */
static void print_cpu_stall_info_end(void)
{
- printk(KERN_ERR "\t");
+ pr_err("\t");
}
/* Zero ->ticks_this_gp for all flavors of RCU. */
@@ -1948,17 +1947,17 @@ static void increment_cpu_stall_ticks(void)
static void print_cpu_stall_info_begin(void)
{
- printk(KERN_CONT " {");
+ pr_cont(" {");
}
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
{
- printk(KERN_CONT " %d", cpu);
+ pr_cont(" %d", cpu);
}
static void print_cpu_stall_info_end(void)
{
- printk(KERN_CONT "} ");
+ pr_cont("} ");
}
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
--
1.8.1.5
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH tip/core/rcu 3/6] rcu: Remove "Experimental" flags
2013-05-20 14:28 ` [PATCH tip/core/rcu 1/6] rcu: Convert rcutree.c printk calls Paul E. McKenney
2013-05-20 14:28 ` [PATCH tip/core/rcu 2/6] rcu: Convert rcutree_plugin.h " Paul E. McKenney
@ 2013-05-20 14:28 ` Paul E. McKenney
2013-05-20 14:28 ` [PATCH tip/core/rcu 4/6] rcu: Drive quiescent-state-forcing delay from HZ Paul E. McKenney
` (2 subsequent siblings)
4 siblings, 0 replies; 7+ messages in thread
From: Paul E. McKenney @ 2013-05-20 14:28 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, laijs, dipankar, akpm, mathieu.desnoyers, josh, niv, tglx,
peterz, rostedt, Valdis.Kletnieks, dhowells, edumazet, darren,
fweisbec, sbw, Paul E. McKenney
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
After a release or two, features are no longer experimental. Therefore,
this commit removes the "Experimental" tag from them.
Reported-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
init/Kconfig | 2 +-
kernel/rcutree_plugin.h | 10 +++++-----
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/init/Kconfig b/init/Kconfig
index 9d3a788..09ab5c2 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -655,7 +655,7 @@ config RCU_BOOST_DELAY
Accept the default if unsure.
config RCU_NOCB_CPU
- bool "Offload RCU callback processing from boot-selected CPUs (EXPERIMENTAL"
+ bool "Offload RCU callback processing from boot-selected CPUs"
depends on TREE_RCU || TREE_PREEMPT_RCU
default n
help
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 207844e..6b3ccaa 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -81,7 +81,7 @@ static void __init rcu_bootup_announce_oddness(void)
pr_info("\tFour-level hierarchy is enabled.\n");
#endif
if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
- pr_info("\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
+ pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
if (nr_cpu_ids != NR_CPUS)
pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
#ifdef CONFIG_RCU_NOCB_CPU
@@ -91,19 +91,19 @@ static void __init rcu_bootup_announce_oddness(void)
have_rcu_nocb_mask = true;
}
#ifdef CONFIG_RCU_NOCB_CPU_ZERO
- pr_info("\tExperimental no-CBs CPU 0\n");
+ pr_info("\tOffload RCU callbacks from CPU 0\n");
cpumask_set_cpu(0, rcu_nocb_mask);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
#ifdef CONFIG_RCU_NOCB_CPU_ALL
- pr_info("\tExperimental no-CBs for all CPUs\n");
+ pr_info("\tOffload RCU callbacks from all CPUs\n");
cpumask_setall(rcu_nocb_mask);
#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
if (have_rcu_nocb_mask) {
cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
- pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf);
+ pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
if (rcu_nocb_poll)
- pr_info("\tExperimental polled no-CBs CPUs.\n");
+ pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
}
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
}
--
1.8.1.5
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH tip/core/rcu 4/6] rcu: Drive quiescent-state-forcing delay from HZ
2013-05-20 14:28 ` [PATCH tip/core/rcu 1/6] rcu: Convert rcutree.c printk calls Paul E. McKenney
2013-05-20 14:28 ` [PATCH tip/core/rcu 2/6] rcu: Convert rcutree_plugin.h " Paul E. McKenney
2013-05-20 14:28 ` [PATCH tip/core/rcu 3/6] rcu: Remove "Experimental" flags Paul E. McKenney
@ 2013-05-20 14:28 ` Paul E. McKenney
2013-05-20 14:28 ` [PATCH tip/core/rcu 5/6] rcu: Merge adjacent identical ifdefs Paul E. McKenney
2013-05-20 14:28 ` [PATCH tip/core/rcu 6/6] rcu: Apply Dave Jones's NOCB Kconfig help feedback Paul E. McKenney
4 siblings, 0 replies; 7+ messages in thread
From: Paul E. McKenney @ 2013-05-20 14:28 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, laijs, dipankar, akpm, mathieu.desnoyers, josh, niv, tglx,
peterz, rostedt, Valdis.Kletnieks, dhowells, edumazet, darren,
fweisbec, sbw, Paul E. McKenney
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Systems with HZ=100 can have slow bootup times due to the default
three-jiffy delays between quiescent-state forcing attempts. This
commit therefore auto-tunes the RCU_JIFFIES_TILL_FORCE_QS value based
on the value of HZ. However, this would break very large systems that
require more time between quiescent-state forcing attempts. This
commit therefore also ups the default delay by one jiffy for each
256 CPUs that might be on the system (based off of nr_cpu_ids at
runtime, -not- NR_CPUS at build time).
Updated to collapse #ifdefs for RCU_JIFFIES_TILL_FORCE_QS into a
step-function definition as suggested by Josh Triplett.
Reported-by: Paul Mackerras <paulus@au1.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
kernel/rcutree.c | 18 ++++++++++++++++--
kernel/rcutree.h | 15 ++++++++++-----
2 files changed, 26 insertions(+), 7 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 302eadf..33510a1 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -218,8 +218,8 @@ module_param(blimit, long, 0444);
module_param(qhimark, long, 0444);
module_param(qlowmark, long, 0444);
-static ulong jiffies_till_first_fqs = RCU_JIFFIES_TILL_FORCE_QS;
-static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS;
+static ulong jiffies_till_first_fqs = ULONG_MAX;
+static ulong jiffies_till_next_fqs = ULONG_MAX;
module_param(jiffies_till_first_fqs, ulong, 0644);
module_param(jiffies_till_next_fqs, ulong, 0644);
@@ -3252,11 +3252,25 @@ static void __init rcu_init_one(struct rcu_state *rsp,
*/
static void __init rcu_init_geometry(void)
{
+ ulong d;
int i;
int j;
int n = nr_cpu_ids;
int rcu_capacity[MAX_RCU_LVLS + 1];
+ /*
+ * Initialize any unspecified boot parameters.
+ * The default values of jiffies_till_first_fqs and
+ * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
+ * value, which is a function of HZ, then adding one for each
+ * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
+ */
+ d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
+ if (jiffies_till_first_fqs == ULONG_MAX)
+ jiffies_till_first_fqs = d;
+ if (jiffies_till_next_fqs == ULONG_MAX)
+ jiffies_till_next_fqs = d;
+
/* If the compile-time values are accurate, just leave. */
if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
nr_cpu_ids == NR_CPUS)
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index da77a8f..cc5b1b7 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -342,12 +342,17 @@ struct rcu_data {
#define RCU_FORCE_QS 3 /* Need to force quiescent state. */
#define RCU_SIGNAL_INIT RCU_SAVE_DYNTICK
-#define RCU_JIFFIES_TILL_FORCE_QS 3 /* for rsp->jiffies_force_qs */
+#define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500))
+ /* For jiffies_till_first_fqs and */
+ /* and jiffies_till_next_fqs. */
-#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time */
- /* to take at least one */
- /* scheduling clock irq */
- /* before ratting on them. */
+#define RCU_JIFFIES_FQS_DIV 256 /* Very large systems need more */
+ /* delay between bouts of */
+ /* quiescent-state forcing. */
+
+#define RCU_STALL_RAT_DELAY 2 /* Allow other CPUs time to take */
+ /* at least one scheduling clock */
+ /* irq before ratting on them. */
#define rcu_wait(cond) \
do { \
--
1.8.1.5
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH tip/core/rcu 5/6] rcu: Merge adjacent identical ifdefs
2013-05-20 14:28 ` [PATCH tip/core/rcu 1/6] rcu: Convert rcutree.c printk calls Paul E. McKenney
` (2 preceding siblings ...)
2013-05-20 14:28 ` [PATCH tip/core/rcu 4/6] rcu: Drive quiescent-state-forcing delay from HZ Paul E. McKenney
@ 2013-05-20 14:28 ` Paul E. McKenney
2013-05-20 14:28 ` [PATCH tip/core/rcu 6/6] rcu: Apply Dave Jones's NOCB Kconfig help feedback Paul E. McKenney
4 siblings, 0 replies; 7+ messages in thread
From: Paul E. McKenney @ 2013-05-20 14:28 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, laijs, dipankar, akpm, mathieu.desnoyers, josh, niv, tglx,
peterz, rostedt, Valdis.Kletnieks, dhowells, edumazet, darren,
fweisbec, sbw, Paul E. McKenney
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Two ifdefs in kernel/rcupdate.c now have identical conditions with
nothing between them, so the commit merges them into a single ifdef.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
kernel/rcupdate.c | 3 ---
1 file changed, 3 deletions(-)
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 48ab703..faeea98 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -145,9 +145,6 @@ static struct lock_class_key rcu_sched_lock_key;
struct lockdep_map rcu_sched_lock_map =
STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
-#endif
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
int debug_lockdep_rcu_enabled(void)
{
--
1.8.1.5
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH tip/core/rcu 6/6] rcu: Apply Dave Jones's NOCB Kconfig help feedback
2013-05-20 14:28 ` [PATCH tip/core/rcu 1/6] rcu: Convert rcutree.c printk calls Paul E. McKenney
` (3 preceding siblings ...)
2013-05-20 14:28 ` [PATCH tip/core/rcu 5/6] rcu: Merge adjacent identical ifdefs Paul E. McKenney
@ 2013-05-20 14:28 ` Paul E. McKenney
4 siblings, 0 replies; 7+ messages in thread
From: Paul E. McKenney @ 2013-05-20 14:28 UTC (permalink / raw)
To: linux-kernel
Cc: mingo, laijs, dipankar, akpm, mathieu.desnoyers, josh, niv, tglx,
peterz, rostedt, Valdis.Kletnieks, dhowells, edumazet, darren,
fweisbec, sbw, Paul E. McKenney
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
The Kconfig help text for the RCU_NOCB_CPU_NONE, RCU_NOCB_CPU_ZERO,
and RCU_NOCB_CPU_ALL Kconfig options was unclear, so this commit
adds a bit more detail.
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
init/Kconfig | 34 +++++++++++++++++++++++++---------
1 file changed, 25 insertions(+), 9 deletions(-)
diff --git a/init/Kconfig b/init/Kconfig
index 09ab5c2..289bb3f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -681,9 +681,10 @@ choice
prompt "Build-forced no-CBs CPUs"
default RCU_NOCB_CPU_NONE
help
- This option allows no-CBs CPUs to be specified at build time.
- Additional no-CBs CPUs may be specified by the rcu_nocbs=
- boot parameter.
+ This option allows no-CBs CPUs (whose RCU callbacks are invoked
+ from kthreads rather than from softirq context) to be specified
+ at build time. Additional no-CBs CPUs may be specified by
+ the rcu_nocbs= boot parameter.
config RCU_NOCB_CPU_NONE
bool "No build_forced no-CBs CPUs"
@@ -691,25 +692,40 @@ config RCU_NOCB_CPU_NONE
help
This option does not force any of the CPUs to be no-CBs CPUs.
Only CPUs designated by the rcu_nocbs= boot parameter will be
- no-CBs CPUs.
+ no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU
+ kthreads whose names begin with "rcuo". All other CPUs will
+ invoke their own RCU callbacks in softirq context.
+
+ Select this option if you want to choose no-CBs CPUs at
+ boot time, for example, to allow testing of different no-CBs
+ configurations without having to rebuild the kernel each time.
config RCU_NOCB_CPU_ZERO
bool "CPU 0 is a build_forced no-CBs CPU"
depends on RCU_NOCB_CPU && !NO_HZ_FULL
help
- This option forces CPU 0 to be a no-CBs CPU. Additional CPUs
- may be designated as no-CBs CPUs using the rcu_nocbs= boot
- parameter will be no-CBs CPUs.
+ This option forces CPU 0 to be a no-CBs CPU, so that its RCU
+ callbacks are invoked by a per-CPU kthread whose name begins
+ with "rcuo". Additional CPUs may be designated as no-CBs
+ CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs.
+ All other CPUs will invoke their own RCU callbacks in softirq
+ context.
Select this if CPU 0 needs to be a no-CBs CPU for real-time
- or energy-efficiency reasons.
+ or energy-efficiency reasons, but the real reason it exists
+ is to ensure that randconfig testing covers mixed systems.
config RCU_NOCB_CPU_ALL
bool "All CPUs are build_forced no-CBs CPUs"
depends on RCU_NOCB_CPU
help
This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs=
- boot parameter will be ignored.
+ boot parameter will be ignored. All CPUs' RCU callbacks will
+ be executed in the context of per-CPU rcuo kthreads created for
+ this purpose. Assuming that the kthreads whose names start with
+ "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter
+ on the remaining CPUs, but might decrease memory locality during
+ RCU-callback invocation, thus potentially degrading throughput.
Select this if all CPUs need to be no-CBs CPUs for real-time
or energy-efficiency reasons.
--
1.8.1.5
^ permalink raw reply related [flat|nested] 7+ messages in thread