| Message ID | 20190913181953.45748-2-cristian.marussi@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Unify SMP stop generic logic to common code | expand |
On 13/09/2019 19:19, Cristian Marussi wrote: > There was a lot of code duplication across architectures regarding the > SMP stop procedures' logic; moreover some of this duplicated code logic > happened to be similarly faulty across a few architectures: while fixing > such logic, move such generic logic as much as possible inside common > code. > > Collect all the common logic related to SMP stop operations into the > common SMP code; any architecture willing to use such centralized logic > can select CONFIG_ARCH_USE_COMMON_STOP=y and provide the related > arch-specific helpers: in such a scenario, those architectures will > transparently start using the common code provided by smp_send_stop() > common function. > > On the other side, Architectures not willing to use common code SMP stop > logic will simply leave CONFIG_ARCH_USE_COMMON_STOP undefined and carry > on executing their local arch-specific smp_send_stop() as before. > > Suggested-by: Dave Martin <Dave.Martin@arm.com> > Signed-off-by: Cristian Marussi <cristian.marussi@arm.com> > --- > v1 --> v2 > - moved related Kconfig to common code inside arch/Kconfig > - introduced additional CONFIG_USE_COMMON_STOP selected by > CONFIG_ARCH_USE_COMMON_STOP > - introduced helpers to let architectures optionally alter > the default common code behaviour while waiting for CPUs: > change timeout or wait for ever. (will be needed by x86) > --- > arch/Kconfig | 7 +++++ > include/linux/smp.h | 55 +++++++++++++++++++++++++++++++++++++ > kernel/smp.c | 67 +++++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 129 insertions(+) > > diff --git a/arch/Kconfig b/arch/Kconfig > index a7b57dd42c26..89766e6c0ac8 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -166,6 +166,13 @@ config ARCH_USE_BUILTIN_BSWAP > instructions should set this. And it shouldn't hurt to set it > on architectures that don't have such instructions. > > +config ARCH_USE_COMMON_SMP_STOP > + def_bool n > + > +config USE_COMMON_SMP_STOP > + depends on SMP && ARCH_USE_COMMON_SMP_STOP > + def_bool y > + > config KRETPROBES > def_bool y > depends on KPROBES && HAVE_KRETPROBES > diff --git a/include/linux/smp.h b/include/linux/smp.h > index 6fc856c9eda5..381a14bfcd96 100644 > --- a/include/linux/smp.h > +++ b/include/linux/smp.h > @@ -77,6 +77,61 @@ int smp_call_function_single_async(int cpu, call_single_data_t *csd); > */ > extern void smp_send_stop(void); > > +#ifdef CONFIG_USE_COMMON_SMP_STOP > +static atomic_t wait_forever; > +static atomic_t wait_timeout = ATOMIC_INIT(USEC_PER_SEC); > + > +/* > + * An Architecture can optionally decide to use this helper to change the > + * waiting behaviour of common STOP logic, forcing to wait forever for > + * all CPUs to be stopped. > + */ > +static inline void smp_stop_set_wait_forever(int wait) > +{ > + atomic_set(&wait_forever, wait); > + /* ensure wait atomic-op is visible */ > + smp_mb__after_atomic(); > +} > + These new helpers I added in V2 to let x86 configure wait/timeout SMP common stop behavior are in fact deadly broken as of now since based on underlying static header-globals. I'll fix in V3. Cheers Cristian > +/* > + * An Architecture can optionally decide to use this helper to change the > + * waiting timeout of common STOP logic. A ZERO timeout means no timeout > + * at all as long as wait_forever was not previously set. > + * > + * Note that wait_forever and timeout must remain individually selectable: > + * so you can temporarily request wait_forever while keeping the same timeout > + * settings. > + */ > +static inline void smp_stop_set_wait_timeout_us(unsigned long timeout) > +{ > + atomic_set(&wait_timeout, timeout); > + /* ensure timeout atomic-op is visible */ > + smp_mb__after_atomic(); > +} > + > +/* Retrieve the current wait settings. */ > +static inline bool smp_stop_get_wait_timeout_us(unsigned long *timeout) > +{ > + if (timeout) > + *timeout = atomic_read(&wait_timeout); > + return atomic_read(&wait_forever); > +} > + > +/* > + * Any Architecture willing to use STOP common logic implementation > + * MUST at least provide the arch_smp_stop_call() helper which is in > + * charge of its own arch-specific CPU-stop mechanism. > + */ > +extern void arch_smp_stop_call(cpumask_t *cpus); > + > +/* > + * An Architecture CAN also provide the arch_smp_cpus_stop_complete() > + * dedicated helper, to perform any final arch-specific operation on > + * the local CPU once the other CPUs have been successfully stopped. > + */ > +void arch_smp_cpus_stop_complete(void); > +#endif > + > /* > * sends a 'reschedule' event to another CPU: > */ > diff --git a/kernel/smp.c b/kernel/smp.c > index 7dbcb402c2fc..72f99bf13fd0 100644 > --- a/kernel/smp.c > +++ b/kernel/smp.c > @@ -20,6 +20,7 @@ > #include <linux/sched.h> > #include <linux/sched/idle.h> > #include <linux/hypervisor.h> > +#include <linux/delay.h> > > #include "smpboot.h" > > @@ -817,3 +818,69 @@ int smp_call_on_cpu(unsigned int cpu, int (*func)(void *), void *par, bool phys) > return sscs.ret; > } > EXPORT_SYMBOL_GPL(smp_call_on_cpu); > + > +#ifdef CONFIG_USE_COMMON_SMP_STOP > +void __weak arch_smp_cpus_stop_complete(void) { } > + > +static inline bool any_other_cpus_online(cpumask_t *mask, > + unsigned int this_cpu_id) > +{ > + cpumask_copy(mask, cpu_online_mask); > + cpumask_clear_cpu(this_cpu_id, mask); > + > + return !cpumask_empty(mask); > +} > + > +/* > + * This centralizes the common logic to: > + * > + * - evaluate which CPUs are online and needs to be notified for stop, > + * while considering properly the status of the calling CPU > + * > + * - call the arch-specific helpers to request the effective stop > + * > + * - wait for the stop operation to be completed across all involved CPUs > + * monitoring the cpu_online_mask > + */ > +void smp_send_stop(void) > +{ > + unsigned int this_cpu_id; > + cpumask_t mask; > + > + this_cpu_id = smp_processor_id(); > + if (any_other_cpus_online(&mask, this_cpu_id)) { > + bool wait; > + unsigned long timeout; > + unsigned int this_cpu_online = cpu_online(this_cpu_id); > + > + if (system_state <= SYSTEM_RUNNING) > + pr_crit("stopping secondary CPUs\n"); > + arch_smp_stop_call(&mask); > + > + /* > + * Defaults to wait up to one second for other CPUs to stop; > + * architectures can modify the default timeout or request > + * to wait forever. > + * > + * Here we rely simply on cpu_online_mask to sync with > + * arch-specific stop code without bloating the code with an > + * additional atomic_t ad-hoc counter. > + * > + * As a consequence we'll need proper explicit memory barriers > + * in case the other CPUs running the arch-specific stop-code > + * would need to commit to memory some data (like saved_regs). > + */ > + wait = smp_stop_get_wait_timeout_us(&timeout); > + while (num_online_cpus() > this_cpu_online && > + (wait || timeout--)) > + udelay(1); > + /* ensure any stopping-CPUs memory access is made visible */ > + smp_rmb(); > + if (num_online_cpus() > this_cpu_online) > + pr_warn("failed to stop secondary CPUs %*pbl\n", > + cpumask_pr_args(cpu_online_mask)); > + } > + /* Perform final (possibly arch-specific) work on this CPU */ > + arch_smp_cpus_stop_complete(); > +} > +#endif >
diff --git a/arch/Kconfig b/arch/Kconfig index a7b57dd42c26..89766e6c0ac8 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -166,6 +166,13 @@ config ARCH_USE_BUILTIN_BSWAP instructions should set this. And it shouldn't hurt to set it on architectures that don't have such instructions. +config ARCH_USE_COMMON_SMP_STOP + def_bool n + +config USE_COMMON_SMP_STOP + depends on SMP && ARCH_USE_COMMON_SMP_STOP + def_bool y + config KRETPROBES def_bool y depends on KPROBES && HAVE_KRETPROBES diff --git a/include/linux/smp.h b/include/linux/smp.h index 6fc856c9eda5..381a14bfcd96 100644 --- a/include/linux/smp.h +++ b/include/linux/smp.h @@ -77,6 +77,61 @@ int smp_call_function_single_async(int cpu, call_single_data_t *csd); */ extern void smp_send_stop(void); +#ifdef CONFIG_USE_COMMON_SMP_STOP +static atomic_t wait_forever; +static atomic_t wait_timeout = ATOMIC_INIT(USEC_PER_SEC); + +/* + * An Architecture can optionally decide to use this helper to change the + * waiting behaviour of common STOP logic, forcing to wait forever for + * all CPUs to be stopped. + */ +static inline void smp_stop_set_wait_forever(int wait) +{ + atomic_set(&wait_forever, wait); + /* ensure wait atomic-op is visible */ + smp_mb__after_atomic(); +} + +/* + * An Architecture can optionally decide to use this helper to change the + * waiting timeout of common STOP logic. A ZERO timeout means no timeout + * at all as long as wait_forever was not previously set. + * + * Note that wait_forever and timeout must remain individually selectable: + * so you can temporarily request wait_forever while keeping the same timeout + * settings. + */ +static inline void smp_stop_set_wait_timeout_us(unsigned long timeout) +{ + atomic_set(&wait_timeout, timeout); + /* ensure timeout atomic-op is visible */ + smp_mb__after_atomic(); +} + +/* Retrieve the current wait settings. */ +static inline bool smp_stop_get_wait_timeout_us(unsigned long *timeout) +{ + if (timeout) + *timeout = atomic_read(&wait_timeout); + return atomic_read(&wait_forever); +} + +/* + * Any Architecture willing to use STOP common logic implementation + * MUST at least provide the arch_smp_stop_call() helper which is in + * charge of its own arch-specific CPU-stop mechanism. + */ +extern void arch_smp_stop_call(cpumask_t *cpus); + +/* + * An Architecture CAN also provide the arch_smp_cpus_stop_complete() + * dedicated helper, to perform any final arch-specific operation on + * the local CPU once the other CPUs have been successfully stopped. + */ +void arch_smp_cpus_stop_complete(void); +#endif + /* * sends a 'reschedule' event to another CPU: */ diff --git a/kernel/smp.c b/kernel/smp.c index 7dbcb402c2fc..72f99bf13fd0 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -20,6 +20,7 @@ #include <linux/sched.h> #include <linux/sched/idle.h> #include <linux/hypervisor.h> +#include <linux/delay.h> #include "smpboot.h" @@ -817,3 +818,69 @@ int smp_call_on_cpu(unsigned int cpu, int (*func)(void *), void *par, bool phys) return sscs.ret; } EXPORT_SYMBOL_GPL(smp_call_on_cpu); + +#ifdef CONFIG_USE_COMMON_SMP_STOP +void __weak arch_smp_cpus_stop_complete(void) { } + +static inline bool any_other_cpus_online(cpumask_t *mask, + unsigned int this_cpu_id) +{ + cpumask_copy(mask, cpu_online_mask); + cpumask_clear_cpu(this_cpu_id, mask); + + return !cpumask_empty(mask); +} + +/* + * This centralizes the common logic to: + * + * - evaluate which CPUs are online and needs to be notified for stop, + * while considering properly the status of the calling CPU + * + * - call the arch-specific helpers to request the effective stop + * + * - wait for the stop operation to be completed across all involved CPUs + * monitoring the cpu_online_mask + */ +void smp_send_stop(void) +{ + unsigned int this_cpu_id; + cpumask_t mask; + + this_cpu_id = smp_processor_id(); + if (any_other_cpus_online(&mask, this_cpu_id)) { + bool wait; + unsigned long timeout; + unsigned int this_cpu_online = cpu_online(this_cpu_id); + + if (system_state <= SYSTEM_RUNNING) + pr_crit("stopping secondary CPUs\n"); + arch_smp_stop_call(&mask); + + /* + * Defaults to wait up to one second for other CPUs to stop; + * architectures can modify the default timeout or request + * to wait forever. + * + * Here we rely simply on cpu_online_mask to sync with + * arch-specific stop code without bloating the code with an + * additional atomic_t ad-hoc counter. + * + * As a consequence we'll need proper explicit memory barriers + * in case the other CPUs running the arch-specific stop-code + * would need to commit to memory some data (like saved_regs). + */ + wait = smp_stop_get_wait_timeout_us(&timeout); + while (num_online_cpus() > this_cpu_online && + (wait || timeout--)) + udelay(1); + /* ensure any stopping-CPUs memory access is made visible */ + smp_rmb(); + if (num_online_cpus() > this_cpu_online) + pr_warn("failed to stop secondary CPUs %*pbl\n", + cpumask_pr_args(cpu_online_mask)); + } + /* Perform final (possibly arch-specific) work on this CPU */ + arch_smp_cpus_stop_complete(); +} +#endif
There was a lot of code duplication across architectures regarding the SMP stop procedures' logic; moreover some of this duplicated code logic happened to be similarly faulty across a few architectures: while fixing such logic, move such generic logic as much as possible inside common code. Collect all the common logic related to SMP stop operations into the common SMP code; any architecture willing to use such centralized logic can select CONFIG_ARCH_USE_COMMON_STOP=y and provide the related arch-specific helpers: in such a scenario, those architectures will transparently start using the common code provided by smp_send_stop() common function. On the other side, Architectures not willing to use common code SMP stop logic will simply leave CONFIG_ARCH_USE_COMMON_STOP undefined and carry on executing their local arch-specific smp_send_stop() as before. Suggested-by: Dave Martin <Dave.Martin@arm.com> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com> --- v1 --> v2 - moved related Kconfig to common code inside arch/Kconfig - introduced additional CONFIG_USE_COMMON_STOP selected by CONFIG_ARCH_USE_COMMON_STOP - introduced helpers to let architectures optionally alter the default common code behaviour while waiting for CPUs: change timeout or wait for ever. (will be needed by x86) --- arch/Kconfig | 7 +++++ include/linux/smp.h | 55 +++++++++++++++++++++++++++++++++++++ kernel/smp.c | 67 +++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 129 insertions(+)