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Subject: Re: [PATCH v2] RISC-V: Show IPI stats
To:     Anup Patel <anup@brainfault.org>,
        Palmer Dabbelt <palmer@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>
Cc:     Christoph Hellwig <hch@infradead.org>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20180912143734.21205-1-anup@brainfault.org>
From:   Atish Patra <atish.patra@wdc.com>
Message-ID: <feb149b3-d046-0074-c59a-c3c7c8c48f04@wdc.com>
Date:   Thu, 13 Sep 2018 10:51:54 -0700
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On 9/12/18 7:37 AM, Anup Patel wrote:
> This patch provides arch_show_interrupts() implementation to
> show IPI stats via /proc/interrupts.
> 
> Now the contents of /proc/interrupts" will look like below:
>             CPU0       CPU1       CPU2       CPU3
>    8:         17          7          6         14  SiFive PLIC   8  virtio0
>   10:         10         10          9         11  SiFive PLIC  10  ttyS0
> IPI0:       170        673        251         79  Rescheduling interrupts
> IPI1:         1         12         27          1  Function call interrupts
> IPI2:         0          0          0          0  CPU wake-up interrupts
> 
> Signed-off-by: Anup Patel <anup@brainfault.org>
> ---
> 
> Changes since v1:
>   - Add stub inline show_ipi_stats() function for !CONFIG_SMP
>   - Make ipi_names[] dynamically sized at compile time
>   - Minor beautification of ipi_names[] using tabs
> 
>   arch/riscv/include/asm/smp.h |  9 +++++++++
>   arch/riscv/kernel/irq.c      |  8 ++++++++
>   arch/riscv/kernel/smp.c      | 30 ++++++++++++++++++++++++++++--
>   3 files changed, 45 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
> index 8145b8657d20..37e909c04f47 100644
> --- a/arch/riscv/include/asm/smp.h
> +++ b/arch/riscv/include/asm/smp.h
> @@ -36,6 +36,8 @@ static inline bool can_hotplug_cpu(void)
>   static inline void arch_send_call_wakeup_ipi(int cpu) { }
>   #endif
>   
> +struct seq_file;
> +
>   #ifdef CONFIG_SMP
>   
>   enum ipi_message_type {
> @@ -48,6 +50,9 @@ enum ipi_message_type {
>   void send_ipi_message(const struct cpumask *to_whom,
>   		      enum ipi_message_type operation);
>   
> +/* print IPI stats */
> +void show_ipi_stats(struct seq_file *p, int prec);
> +
>   /* SMP initialization hook for setup_arch */
>   void __init setup_smp(void);
>   
> @@ -75,6 +80,10 @@ void boot_sec_cpu(void);
>   
>   #else
>   
> +static inline void show_ipi_stats(struct seq_file *p, int prec)
> +{
> +}
> +
>   static inline int riscv_hartid_to_cpuid(int hartid)
>   {
>   	return 0;
> diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
> index 7e14b0d9a71d..96202139ade5 100644
> --- a/arch/riscv/kernel/irq.c
> +++ b/arch/riscv/kernel/irq.c
> @@ -8,6 +8,8 @@
>   #include <linux/interrupt.h>
>   #include <linux/irqchip.h>
>   #include <linux/irqdomain.h>
> +#include <linux/seq_file.h>
> +#include <asm/smp.h>
>   
>   /*
>    * Possible interrupt causes:
> @@ -24,6 +26,12 @@
>    */
>   #define INTERRUPT_CAUSE_FLAG	(1UL << (__riscv_xlen - 1))
>   
> +int arch_show_interrupts(struct seq_file *p, int prec)
> +{
> +	show_ipi_stats(p, prec);
> +	return 0;
> +}
> +
>   asmlinkage void __irq_entry do_IRQ(struct pt_regs *regs, unsigned long cause)
>   {
>   	struct pt_regs *old_regs = set_irq_regs(regs);
> diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c
> index 629456bb6122..70fd1351d6d9 100644
> --- a/arch/riscv/kernel/smp.c
> +++ b/arch/riscv/kernel/smp.c
> @@ -22,6 +22,7 @@
>   #include <linux/interrupt.h>
>   #include <linux/smp.h>
>   #include <linux/sched.h>
> +#include <linux/seq_file.h>
>   
>   #include <asm/sbi.h>
>   #include <asm/tlbflush.h>
> @@ -29,6 +30,7 @@
>   
>   /* A collection of single bit ipi messages.  */
>   static struct {
> +	unsigned long stats[IPI_MAX] ____cacheline_aligned;
>   	unsigned long bits ____cacheline_aligned;
>   } ipi_data[NR_CPUS] __cacheline_aligned;
>   
> @@ -61,6 +63,7 @@ int setup_profiling_timer(unsigned int multiplier)
>   void riscv_software_interrupt(void)
>   {
>   	unsigned long *pending_ipis = &ipi_data[smp_processor_id()].bits;
> +	unsigned long *stats = ipi_data[smp_processor_id()].stats;
>   
>   	/* Clear pending IPI */
>   	csr_clear(sip, SIE_SSIE);
> @@ -75,11 +78,15 @@ void riscv_software_interrupt(void)
>   		if (ops == 0)
>   			return;
>   
> -		if (ops & (1 << IPI_RESCHEDULE))
> +		if (ops & (1 << IPI_RESCHEDULE)) {
> +			stats[IPI_RESCHEDULE]++;
>   			scheduler_ipi();
> +		}
>   
> -		if (ops & (1 << IPI_CALL_FUNC))
> +		if (ops & (1 << IPI_CALL_FUNC)) {
> +			stats[IPI_CALL_FUNC]++;
>   			generic_smp_call_function_interrupt();
> +		}
>   
>   		BUG_ON((ops >> IPI_MAX) != 0);
>   
> @@ -105,6 +112,25 @@ send_ipi_message(const struct cpumask *to_whom, enum ipi_message_type operation)
>   	sbi_send_ipi(cpumask_bits(&hartid_mask));
>   }
>   
> +static const char *ipi_names[] = {
> +	[IPI_RESCHEDULE]	= "Rescheduling interrupts",
> +	[IPI_CALL_FUNC]		= "Function call interrupts",
> +	[IPI_CALL_WAKEUP]	= "CPU wake-up interrupts",

There were some concerns about cpu hotplug patch which introduced 
IPI_CALL_WAKEUP. I have dropped it as of now from my series. I will send 
it as a separate patch. So we may want to add IPI_CALL_WAKEUP along with 
cpu hotplug patch which makes more sense to me.

Other than that, LGTM.

Regards,
Atish
> +};
> +
> +void show_ipi_stats(struct seq_file *p, int prec)
> +{
> +	unsigned int cpu, i;
> +
> +	for (i = 0; i < IPI_MAX; i++) {
> +		seq_printf(p, "%*s%u:%s", prec - 1, "IPI", i,
> +			   prec >= 4 ? " " : "");
> +		for_each_online_cpu(cpu)
> +			seq_printf(p, "%10lu ", ipi_data[cpu].stats[i]);
> +		seq_printf(p, " %s\n", ipi_names[i]);
> +	}
> +}
> +
>   void arch_send_call_function_ipi_mask(struct cpumask *mask)
>   {
>   	send_ipi_message(mask, IPI_CALL_FUNC);
>