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Date: Fri, 24 Jul 2020 11:01:04 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, torvalds@...ux-foundation.org,
linux-kernel@...r.kernel.org, will@...nel.org, hch@....de,
axboe@...nel.dk, chris@...is-wilson.co.uk, davem@...emloft.net,
kuba@...nel.org, fweisbec@...il.com, oleg@...hat.com
Subject: Re: [RFC][PATCH 2/9] smp: Cleanup smp_call_function*()
On Wed, Jul 22, 2020 at 05:01:51PM +0200, Peter Zijlstra wrote:
> Get rid of the __call_single_node union and cleanup the API a little
> to avoid external code relying on the structure layout as much.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Paul E. McKenney <paulmck@...nel.org>
> ---
> arch/mips/kernel/process.c | 5 +--
> arch/mips/kernel/smp.c | 25 +++------------
> arch/s390/pci/pci_irq.c | 4 --
> arch/x86/kernel/cpuid.c | 7 +---
> arch/x86/lib/msr-smp.c | 7 +---
> block/blk-mq.c | 4 --
> drivers/cpuidle/coupled.c | 3 -
> drivers/net/ethernet/cavium/liquidio/lio_core.c | 9 +----
> include/linux/smp.h | 16 +++++----
> kernel/debug/debug_core.c | 6 +--
> kernel/sched/core.c | 12 +------
> kernel/smp.c | 40 ++++++++++++------------
> net/core/dev.c | 3 -
> 13 files changed, 55 insertions(+), 86 deletions(-)
>
> --- a/arch/mips/kernel/process.c
> +++ b/arch/mips/kernel/process.c
> @@ -687,7 +687,6 @@ unsigned long arch_align_stack(unsigned
> return sp & ALMASK;
> }
>
> -static DEFINE_PER_CPU(call_single_data_t, backtrace_csd);
> static struct cpumask backtrace_csd_busy;
>
> static void handle_backtrace(void *info)
> @@ -696,6 +695,9 @@ static void handle_backtrace(void *info)
> cpumask_clear_cpu(smp_processor_id(), &backtrace_csd_busy);
> }
>
> +static DEFINE_PER_CPU(call_single_data_t, backtrace_csd) =
> + CSD_INIT(handle_backtrace, NULL);
> +
> static void raise_backtrace(cpumask_t *mask)
> {
> call_single_data_t *csd;
> @@ -715,7 +717,6 @@ static void raise_backtrace(cpumask_t *m
> }
>
> csd = &per_cpu(backtrace_csd, cpu);
> - csd->func = handle_backtrace;
> smp_call_function_single_async(cpu, csd);
> }
> }
> --- a/arch/mips/kernel/smp.c
> +++ b/arch/mips/kernel/smp.c
> @@ -687,36 +687,23 @@ EXPORT_SYMBOL(flush_tlb_one);
>
> #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
>
> -static DEFINE_PER_CPU(call_single_data_t, tick_broadcast_csd);
> -
> -void tick_broadcast(const struct cpumask *mask)
> -{
> - call_single_data_t *csd;
> - int cpu;
> -
> - for_each_cpu(cpu, mask) {
> - csd = &per_cpu(tick_broadcast_csd, cpu);
> - smp_call_function_single_async(cpu, csd);
> - }
> -}
> -
> static void tick_broadcast_callee(void *info)
> {
> tick_receive_broadcast();
> }
>
> -static int __init tick_broadcast_init(void)
> +static DEFINE_PER_CPU(call_single_data_t, tick_broadcast_csd) =
> + CSD_INIT(tick_broadcast_callee, NULL);
> +
> +void tick_broadcast(const struct cpumask *mask)
> {
> call_single_data_t *csd;
> int cpu;
>
> - for (cpu = 0; cpu < NR_CPUS; cpu++) {
> + for_each_cpu(cpu, mask) {
> csd = &per_cpu(tick_broadcast_csd, cpu);
> - csd->func = tick_broadcast_callee;
> + smp_call_function_single_async(cpu, csd);
> }
> -
> - return 0;
> }
> -early_initcall(tick_broadcast_init);
>
> #endif /* CONFIG_GENERIC_CLOCKEVENTS_BROADCAST */
> --- a/arch/s390/pci/pci_irq.c
> +++ b/arch/s390/pci/pci_irq.c
> @@ -178,9 +178,7 @@ static void zpci_handle_fallback_irq(voi
> if (atomic_inc_return(&cpu_data->scheduled) > 1)
> continue;
>
> - cpu_data->csd.func = zpci_handle_remote_irq;
> - cpu_data->csd.info = &cpu_data->scheduled;
> - cpu_data->csd.flags = 0;
> + INIT_CSD(&cpu_data->csd, zpci_handle_remote_irq, &cpu_data->scheduled);
> smp_call_function_single_async(cpu, &cpu_data->csd);
> }
> }
> --- a/arch/x86/kernel/cpuid.c
> +++ b/arch/x86/kernel/cpuid.c
> @@ -74,10 +74,9 @@ static ssize_t cpuid_read(struct file *f
>
> init_completion(&cmd.done);
> for (; count; count -= 16) {
> - call_single_data_t csd = {
> - .func = cpuid_smp_cpuid,
> - .info = &cmd,
> - };
> + call_single_data_t csd;
> +
> + INIT_CSD(&csd, cpuid_smp_cpuid, &cmd);
>
> cmd.regs.eax = pos;
> cmd.regs.ecx = pos >> 32;
> --- a/arch/x86/lib/msr-smp.c
> +++ b/arch/x86/lib/msr-smp.c
> @@ -169,12 +169,11 @@ static void __wrmsr_safe_on_cpu(void *in
> int rdmsr_safe_on_cpu(unsigned int cpu, u32 msr_no, u32 *l, u32 *h)
> {
> struct msr_info_completion rv;
> - call_single_data_t csd = {
> - .func = __rdmsr_safe_on_cpu,
> - .info = &rv,
> - };
> + call_single_data_t csd;
> int err;
>
> + INIT_CSD(&csd, __rdmsr_safe_on_cpu, &rv);
> +
> memset(&rv, 0, sizeof(rv));
> init_completion(&rv.done);
> rv.msr.msr_no = msr_no;
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -672,9 +672,7 @@ bool blk_mq_complete_request_remote(stru
> return false;
>
> if (blk_mq_complete_need_ipi(rq)) {
> - rq->csd.func = __blk_mq_complete_request_remote;
> - rq->csd.info = rq;
> - rq->csd.flags = 0;
> + INIT_CSD(&rq->csd, __blk_mq_complete_request_remote, rq);
> smp_call_function_single_async(rq->mq_ctx->cpu, &rq->csd);
> } else {
> if (rq->q->nr_hw_queues > 1)
> --- a/drivers/cpuidle/coupled.c
> +++ b/drivers/cpuidle/coupled.c
> @@ -674,8 +674,7 @@ int cpuidle_coupled_register_device(stru
> coupled->refcnt++;
>
> csd = &per_cpu(cpuidle_coupled_poke_cb, dev->cpu);
> - csd->func = cpuidle_coupled_handle_poke;
> - csd->info = (void *)(unsigned long)dev->cpu;
> + INIT_CSD(csd, cpuidle_coupled_handle_poke, (void *)(unsigned long)dev->cpu);
>
> return 0;
> }
> --- a/drivers/net/ethernet/cavium/liquidio/lio_core.c
> +++ b/drivers/net/ethernet/cavium/liquidio/lio_core.c
> @@ -726,13 +726,8 @@ static void liquidio_napi_drv_callback(v
> droq->cpu_id == this_cpu) {
> napi_schedule_irqoff(&droq->napi);
> } else {
> - call_single_data_t *csd = &droq->csd;
> -
> - csd->func = napi_schedule_wrapper;
> - csd->info = &droq->napi;
> - csd->flags = 0;
> -
> - smp_call_function_single_async(droq->cpu_id, csd);
> + INIT_CSD(&droq->csd, napi_schedule_wrapper, &droq->napi);
> + smp_call_function_single_async(droq->cpu_id, &droq->csd);
> }
> }
>
> --- a/include/linux/smp.h
> +++ b/include/linux/smp.h
> @@ -21,21 +21,23 @@ typedef bool (*smp_cond_func_t)(int cpu,
> * structure shares (partial) layout with struct irq_work
> */
> struct __call_single_data {
> - union {
> - struct __call_single_node node;
> - struct {
> - struct llist_node llist;
> - unsigned int flags;
> - };
> - };
> + struct __call_single_node node;
> smp_call_func_t func;
> void *info;
> };
>
> +#define CSD_INIT(_func, _info) \
> + (struct __call_single_data){ .func = (_func), .info = (_info), }
> +
> /* Use __aligned() to avoid to use 2 cache lines for 1 csd */
> typedef struct __call_single_data call_single_data_t
> __aligned(sizeof(struct __call_single_data));
>
> +#define INIT_CSD(_csd, _func, _info) \
> +do { \
> + *(_csd) = CSD_INIT((_func), (_info)); \
> +} while (0)
> +
> /*
> * Enqueue a llist_node on the call_single_queue; be very careful, read
> * flush_smp_call_function_queue() in detail.
> --- a/kernel/debug/debug_core.c
> +++ b/kernel/debug/debug_core.c
> @@ -225,8 +225,6 @@ int __weak kgdb_skipexception(int except
> * Default (weak) implementation for kgdb_roundup_cpus
> */
>
> -static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd);
> -
> void __weak kgdb_call_nmi_hook(void *ignored)
> {
> /*
> @@ -240,6 +238,9 @@ void __weak kgdb_call_nmi_hook(void *ign
> kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
> }
>
> +static DEFINE_PER_CPU(call_single_data_t, kgdb_roundup_csd) =
> + CSD_INIT(kgdb_call_nmi_hook, NULL);
> +
> void __weak kgdb_roundup_cpus(void)
> {
> call_single_data_t *csd;
> @@ -266,7 +267,6 @@ void __weak kgdb_roundup_cpus(void)
> continue;
> kgdb_info[cpu].rounding_up = true;
>
> - csd->func = kgdb_call_nmi_hook;
> ret = smp_call_function_single_async(cpu, csd);
> if (ret)
> kgdb_info[cpu].rounding_up = false;
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -223,14 +223,6 @@ void update_rq_clock(struct rq *rq)
> update_rq_clock_task(rq, delta);
> }
>
> -static inline void
> -rq_csd_init(struct rq *rq, call_single_data_t *csd, smp_call_func_t func)
> -{
> - csd->flags = 0;
> - csd->func = func;
> - csd->info = rq;
> -}
> -
> #ifdef CONFIG_SCHED_HRTICK
> /*
> * Use HR-timers to deliver accurate preemption points.
> @@ -331,7 +323,7 @@ void hrtick_start(struct rq *rq, u64 del
> static void hrtick_rq_init(struct rq *rq)
> {
> #ifdef CONFIG_SMP
> - rq_csd_init(rq, &rq->hrtick_csd, __hrtick_start);
> + INIT_CSD(&rq->hrtick_csd, __hrtick_start, rq);
> #endif
> hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
> rq->hrtick_timer.function = hrtick;
> @@ -6835,7 +6827,7 @@ void __init sched_init(void)
> rq->last_blocked_load_update_tick = jiffies;
> atomic_set(&rq->nohz_flags, 0);
>
> - rq_csd_init(rq, &rq->nohz_csd, nohz_csd_func);
> + INIT_CSD(&rq->nohz_csd, nohz_csd_func, rq);
> #endif
> #endif /* CONFIG_SMP */
> hrtick_rq_init(rq);
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -24,7 +24,7 @@
> #include "smpboot.h"
> #include "sched/smp.h"
>
> -#define CSD_TYPE(_csd) ((_csd)->flags & CSD_FLAG_TYPE_MASK)
> +#define CSD_TYPE(_csd) ((_csd)->node.u_flags & CSD_FLAG_TYPE_MASK)
>
> struct call_function_data {
> call_single_data_t __percpu *csd;
> @@ -105,13 +105,13 @@ void __init call_function_init(void)
> */
> static __always_inline void csd_lock_wait(call_single_data_t *csd)
> {
> - smp_cond_load_acquire(&csd->flags, !(VAL & CSD_FLAG_LOCK));
> + smp_cond_load_acquire(&csd->node.u_flags, !(VAL & CSD_FLAG_LOCK));
> }
>
> static __always_inline void csd_lock(call_single_data_t *csd)
> {
> csd_lock_wait(csd);
> - csd->flags |= CSD_FLAG_LOCK;
> + csd->node.u_flags |= CSD_FLAG_LOCK;
>
> /*
> * prevent CPU from reordering the above assignment
> @@ -123,12 +123,12 @@ static __always_inline void csd_lock(cal
>
> static __always_inline void csd_unlock(call_single_data_t *csd)
> {
> - WARN_ON(!(csd->flags & CSD_FLAG_LOCK));
> + WARN_ON(!(csd->node.u_flags & CSD_FLAG_LOCK));
>
> /*
> * ensure we're all done before releasing data:
> */
> - smp_store_release(&csd->flags, 0);
> + smp_store_release(&csd->node.u_flags, 0);
> }
>
> static DEFINE_PER_CPU_SHARED_ALIGNED(call_single_data_t, csd_data);
> @@ -178,7 +178,7 @@ static int generic_exec_single(int cpu,
> return -ENXIO;
> }
>
> - __smp_call_single_queue(cpu, &csd->llist);
> + __smp_call_single_queue(cpu, &csd->node.llist);
>
> return 0;
> }
> @@ -231,7 +231,7 @@ static void flush_smp_call_function_queu
> * We don't have to use the _safe() variant here
> * because we are not invoking the IPI handlers yet.
> */
> - llist_for_each_entry(csd, entry, llist) {
> + llist_for_each_entry(csd, entry, node.llist) {
> switch (CSD_TYPE(csd)) {
> case CSD_TYPE_ASYNC:
> case CSD_TYPE_SYNC:
> @@ -256,22 +256,22 @@ static void flush_smp_call_function_queu
> * First; run all SYNC callbacks, people are waiting for us.
> */
> prev = NULL;
> - llist_for_each_entry_safe(csd, csd_next, entry, llist) {
> + llist_for_each_entry_safe(csd, csd_next, entry, node.llist) {
> /* Do we wait until *after* callback? */
> if (CSD_TYPE(csd) == CSD_TYPE_SYNC) {
> smp_call_func_t func = csd->func;
> void *info = csd->info;
>
> if (prev) {
> - prev->next = &csd_next->llist;
> + prev->next = &csd_next->node.llist;
> } else {
> - entry = &csd_next->llist;
> + entry = &csd_next->node.llist;
> }
>
> func(info);
> csd_unlock(csd);
> } else {
> - prev = &csd->llist;
> + prev = &csd->node.llist;
> }
> }
>
> @@ -282,14 +282,14 @@ static void flush_smp_call_function_queu
> * Second; run all !SYNC callbacks.
> */
> prev = NULL;
> - llist_for_each_entry_safe(csd, csd_next, entry, llist) {
> + llist_for_each_entry_safe(csd, csd_next, entry, node.llist) {
> int type = CSD_TYPE(csd);
>
> if (type != CSD_TYPE_TTWU) {
> if (prev) {
> - prev->next = &csd_next->llist;
> + prev->next = &csd_next->node.llist;
> } else {
> - entry = &csd_next->llist;
> + entry = &csd_next->node.llist;
> }
>
> if (type == CSD_TYPE_ASYNC) {
> @@ -303,7 +303,7 @@ static void flush_smp_call_function_queu
> }
>
> } else {
> - prev = &csd->llist;
> + prev = &csd->node.llist;
> }
> }
>
> @@ -339,7 +339,7 @@ int smp_call_function_single(int cpu, sm
> {
> call_single_data_t *csd;
> call_single_data_t csd_stack = {
> - .flags = CSD_FLAG_LOCK | CSD_TYPE_SYNC,
> + .node = { .u_flags = CSD_FLAG_LOCK | CSD_TYPE_SYNC, },
> };
> int this_cpu;
> int err;
> @@ -414,12 +414,12 @@ int smp_call_function_single_async(int c
>
> preempt_disable();
>
> - if (csd->flags & CSD_FLAG_LOCK) {
> + if (csd->node.u_flags & CSD_FLAG_LOCK) {
> err = -EBUSY;
> goto out;
> }
>
> - csd->flags = CSD_FLAG_LOCK;
> + csd->node.u_flags = CSD_FLAG_LOCK;
> smp_wmb();
>
> err = generic_exec_single(cpu, csd);
> @@ -537,10 +537,10 @@ static void smp_call_function_many_cond(
>
> csd_lock(csd);
> if (wait)
> - csd->flags |= CSD_TYPE_SYNC;
> + csd->node.u_flags |= CSD_TYPE_SYNC;
> csd->func = func;
> csd->info = info;
> - if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))
> + if (llist_add(&csd->node.llist, &per_cpu(call_single_queue, cpu)))
> __cpumask_set_cpu(cpu, cfd->cpumask_ipi);
> }
>
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -10661,8 +10661,7 @@ static int __init net_dev_init(void)
> INIT_LIST_HEAD(&sd->poll_list);
> sd->output_queue_tailp = &sd->output_queue;
> #ifdef CONFIG_RPS
> - sd->csd.func = rps_trigger_softirq;
> - sd->csd.info = sd;
> + INIT_CSD(&sd->csd, rps_trigger_softirq, sd);
> sd->cpu = i;
> #endif
>
>
>
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