Re: [RFC][PATCH 7/9] smp,irq_work: Use the new irq_work API

Paul E. McKenney
2020-07-22T22:09:47Z

On Wed, Jul 22, 2020 at 05:01:56PM +0200, Peter Zijlstra wrote:
> Convert the performance sensitive users of
> smp_call_single_function_async() over to the new
> irq_work_queue_remote_static().
>
> The new API is marginally less crap but taking these users away allows
> fixing up smp_call_single_function_async() without risk of performance
> regressions.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

But given that kvm.sh gives a return status like "git bisect run",
why not bisect?

And bisection converged on this patch with a similar splat.

Decoding the assembly makes it appear that nohz_work_func() got a bogus
pointer having a rather odd value of 0x200000001.

Thanx, Paul

------------------------------------------------------------------------

0: e8 35 52 ff ff call 0xffffffffffff523a
5: 48 89 c3 mov rbx,rax
8: eb 93 jmp 0xffffffffffffff9d
a: 8b 43 70 mov eax,DWORD PTR [rbx+0x70]
d: 89 44 24 04 mov DWORD PTR [rsp+0x4],eax
11: eb c2 jmp 0xffffffffffffffd5
13: 48 c7 c0 ea ff ff ff mov rax,0xffffffffffffffea
1a: eb 94 jmp 0xffffffffffffffb0
1c: e8 c9 02 a7 00 call 0xa702ea
21: 66 0f 1f 84 00 00 00 nop WORD PTR [rax+rax*1+0x0]
28: 00 00
2a: 4c 63 8f f0 09 00 00 movsxd r9,DWORD PTR [rdi+0x9f0] <-------
31: 48 c7 c1 00 91 02 00 mov rcx,0x29100
38: 48 89 ca mov rdx,rcx

> ---
> block/blk-mq.c | 8 ++++----
> include/linux/blkdev.h | 4 ++--
> include/linux/netdevice.h | 3 ++-
> kernel/sched/core.c | 16 ++++++++--------
> kernel/sched/fair.c | 6 +++---
> kernel/sched/sched.h | 4 ++--
> net/core/dev.c | 15 ++++++++++-----
> 7 files changed, 31 insertions(+), 25 deletions(-)
>
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -623,9 +623,9 @@ static int blk_softirq_cpu_dead(unsigned
> }
>
>
> -static void __blk_mq_complete_request_remote(void *data)
> +static void __blk_mq_complete_request_remote(struct irq_work *work)
> {
> - struct request *rq = data;
> + struct request *rq = container_of(work, struct request, work);
>
> /*
> * For most of single queue controllers, there is only one irq vector
> @@ -672,8 +672,8 @@ bool blk_mq_complete_request_remote(stru
> return false;
>
> if (blk_mq_complete_need_ipi(rq)) {
> - INIT_CSD(&rq->csd, __blk_mq_complete_request_remote, rq);
> - smp_call_function_single_async(rq->mq_ctx->cpu, &rq->csd);
> + rq->work = IRQ_WORK_INIT_HARD(__blk_mq_complete_request_remote);
> + irq_work_queue_remote_static(rq->mq_ctx->cpu, &rq->work);
> } else {
> if (rq->q->nr_hw_queues > 1)
> return false;
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -19,7 +19,7 @@
> #include <linux/stringify.h>
> #include <linux/gfp.h>
> #include <linux/bsg.h>
> -#include <linux/smp.h>
> +#include <linux/irq_work.h>
> #include <linux/rcupdate.h>
> #include <linux/percpu-refcount.h>
> #include <linux/scatterlist.h>
> @@ -234,7 +234,7 @@ struct request {
> unsigned long deadline;
>
> union {
> - struct __call_single_data csd;
> + struct irq_work work;
> u64 fifo_time;
> };
>
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -26,6 +26,7 @@
> #include <linux/delay.h>
> #include <linux/atomic.h>
> #include <linux/prefetch.h>
> +#include <linux/irq_work.h>
> #include <asm/cache.h>
> #include <asm/byteorder.h>
>
> @@ -3126,7 +3127,7 @@ struct softnet_data {
> unsigned int input_queue_head ____cacheline_aligned_in_smp;
>
> /* Elements below can be accessed between CPUs for RPS/RFS */
> - call_single_data_t csd ____cacheline_aligned_in_smp;
> + struct irq_work work ____cacheline_aligned_in_smp;
> struct softnet_data *rps_ipi_next;
> unsigned int cpu;
> unsigned int input_queue_tail;
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -265,9 +265,9 @@ static void __hrtick_restart(struct rq *
> /*
> * called from hardirq (IPI) context
> */
> -static void __hrtick_start(void *arg)
> +static void __hrtick_start(struct irq_work *work)
> {
> - struct rq *rq = arg;
> + struct rq *rq = container_of(work, struct rq, hrtick_work);
> struct rq_flags rf;
>
> rq_lock(rq, &rf);
> @@ -298,7 +298,7 @@ void hrtick_start(struct rq *rq, u64 del
> if (rq == this_rq())
> __hrtick_restart(rq);
> else
> - smp_call_function_single_async(cpu_of(rq), &rq->hrtick_csd);
> + irq_work_queue_remote_static(cpu_of(rq), &rq->hrtick_work);
> }
>
> #else
> @@ -323,7 +323,7 @@ void hrtick_start(struct rq *rq, u64 del
> static void hrtick_rq_init(struct rq *rq)
> {
> #ifdef CONFIG_SMP
> - INIT_CSD(&rq->hrtick_csd, __hrtick_start, rq);
> + rq->hrtick_work = IRQ_WORK_INIT_HARD(__hrtick_start);
> #endif
> hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
> rq->hrtick_timer.function = hrtick;
> @@ -633,14 +633,14 @@ void wake_up_nohz_cpu(int cpu)
> wake_up_idle_cpu(cpu);
> }
>
> -static void nohz_csd_func(void *info)
> +static void nohz_work_func(struct irq_work *work)
> {
> - struct rq *rq = info;
> + struct rq *rq = container_of(work, struct rq, nohz_work);
> int cpu = cpu_of(rq);
> unsigned int flags;
>
> /*
> - * Release the rq::nohz_csd.
> + * Release rq::nohz_work.
> */
> flags = atomic_fetch_andnot(NOHZ_KICK_MASK, nohz_flags(cpu));
> WARN_ON(!(flags & NOHZ_KICK_MASK));
> @@ -6827,7 +6827,7 @@ void __init sched_init(void)
> rq->last_blocked_load_update_tick = jiffies;
> atomic_set(&rq->nohz_flags, 0);
>
> - INIT_CSD(&rq->nohz_csd, nohz_csd_func, rq);
> + rq->nohz_work = IRQ_WORK_INIT_HARD(nohz_work_func);
> #endif
> #endif /* CONFIG_SMP */
> hrtick_rq_init(rq);
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10039,8 +10039,8 @@ static void kick_ilb(unsigned int flags)
> return;
>
> /*
> - * Access to rq::nohz_csd is serialized by NOHZ_KICK_MASK; he who sets
> - * the first flag owns it; cleared by nohz_csd_func().
> + * Access to rq::nohz_work is serialized by NOHZ_KICK_MASK; he who sets
> + * the first flag owns it; cleared by nohz_work_func().
> */
> flags = atomic_fetch_or(flags, nohz_flags(ilb_cpu));
> if (flags & NOHZ_KICK_MASK)
> @@ -10051,7 +10051,7 @@ static void kick_ilb(unsigned int flags)
> * is idle. And the softirq performing nohz idle load balance
> * will be run before returning from the IPI.
> */
> - smp_call_function_single_async(ilb_cpu, &cpu_rq(ilb_cpu)->nohz_csd);
> + irq_work_queue_remote_static(ilb_cpu, &cpu_rq(ilb_cpu)->nohz_work);
> }
>
> /*
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -904,7 +904,7 @@ struct rq {
> #ifdef CONFIG_SMP
> unsigned long last_blocked_load_update_tick;
> unsigned int has_blocked_load;
> - call_single_data_t nohz_csd;
> + struct irq_work nohz_work;
> #endif /* CONFIG_SMP */
> unsigned int nohz_tick_stopped;
> atomic_t nohz_flags;
> @@ -1015,7 +1015,7 @@ struct rq {
>
> #ifdef CONFIG_SCHED_HRTICK
> #ifdef CONFIG_SMP
> - call_single_data_t hrtick_csd;
> + struct irq_work hrtick_work;
> #endif
> struct hrtimer hrtick_timer;
> #endif
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4444,9 +4444,9 @@ EXPORT_SYMBOL(rps_may_expire_flow);
> #endif /* CONFIG_RFS_ACCEL */
>
> /* Called from hardirq (IPI) context */
> -static void rps_trigger_softirq(void *data)
> +static void rps_trigger_softirq(struct irq_work *work)
> {
> - struct softnet_data *sd = data;
> + struct softnet_data *sd = container_of(work, struct softnet_data, work);
>
> ____napi_schedule(sd, &sd->backlog);
> sd->received_rps++;
> @@ -6185,8 +6185,13 @@ static void net_rps_send_ipi(struct soft
> while (remsd) {
> struct softnet_data *next = remsd->rps_ipi_next;
>
> - if (cpu_online(remsd->cpu))
> - smp_call_function_single_async(remsd->cpu, &remsd->csd);
> + if (cpu_online(remsd->cpu)) {
> + /*
> + * XXX can there be two CPUs calling into the same remsd?
> + * XXX serialized by NAPI_STATE_SCHED ??
> + */
> + irq_work_queue_remote_static(remsd->cpu, &remsd->work);
> + }
> remsd = next;
> }
> #endif
> @@ -10661,7 +10666,7 @@ static int __init net_dev_init(void)
> INIT_LIST_HEAD(&sd->poll_list);
> sd->output_queue_tailp = &sd->output_queue;
> #ifdef CONFIG_RPS
> - INIT_CSD(&sd->csd, rps_trigger_softirq, sd);
> + init_irq_work(&sd->work, rps_trigger_softirq);
> sd->cpu = i;
> #endif
>
>
>