linux-kernel - Re: [PATCH] MIPS: Loongson64: Switch to SYNC

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Message-Id: <e68b7f44-8a3c-4963-8d95-be8747bf9a61@app.fastmail.com>
Date: Thu, 18 Jul 2024 15:34:30 +0800
From: "Jiaxun Yang" <jiaxun.yang@...goat.com>
To: "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 "Huacai Chen" <chenhuacai@...nel.org>
Cc: "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: Loongson64: Switch to SYNC_R4K



在2024年7月14日七月 上午10:41，Jiaxun Yang写道：
> Nowadays SYNC_R4K is performing better than Loongson64's
> custom sync mechanism.
>
> Switch to SYNC_R4K to improve performance and reduce code
> duplication.
>
> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
> ---
> Last minute for 6.11 :-)

Hi Thomas,

Could you please apply this to 6.11 PR, or 6.11 fixes?

This is technically a left over of previous clock source series, and it does help
on preventing random RCU stall for multi-node Loongson-3 systems.

Thanks
- Jiaxun

> ---
>  arch/mips/Kconfig           |  1 +
>  arch/mips/include/asm/smp.h |  1 -
>  arch/mips/loongson64/smp.c  | 35 ++---------------------------------
>  3 files changed, 3 insertions(+), 34 deletions(-)
>
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 1236ea122061..e163059dd4d3 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -478,6 +478,7 @@ config MACH_LOONGSON64
>  	select BOARD_SCACHE
>  	select CSRC_R4K
>  	select CEVT_R4K
> +	select SYNC_R4K
>  	select FORCE_PCI
>  	select ISA
>  	select I8259
> diff --git a/arch/mips/include/asm/smp.h b/arch/mips/include/asm/smp.h
> index bc2c240f414b..2427d76f953f 100644
> --- a/arch/mips/include/asm/smp.h
> +++ b/arch/mips/include/asm/smp.h
> @@ -50,7 +50,6 @@ extern int __cpu_logical_map[NR_CPUS];
>  #define SMP_CALL_FUNCTION	0x2
>  /* Octeon - Tell another core to flush its icache */
>  #define SMP_ICACHE_FLUSH	0x4
> -#define SMP_ASK_C0COUNT		0x8
> 
>  /* Mask of CPUs which are currently definitely operating coherently */
>  extern cpumask_t cpu_coherent_mask;
> diff --git a/arch/mips/loongson64/smp.c b/arch/mips/loongson64/smp.c
> index 66d049cdcf14..147acd972a07 100644
> --- a/arch/mips/loongson64/smp.c
> +++ b/arch/mips/loongson64/smp.c
> @@ -33,7 +33,6 @@ static void __iomem *ipi_clear0_regs[16];
>  static void __iomem *ipi_status0_regs[16];
>  static void __iomem *ipi_en0_regs[16];
>  static void __iomem *ipi_mailbox_buf[16];
> -static uint32_t core0_c0count[NR_CPUS];
> 
>  static u32 (*ipi_read_clear)(int cpu);
>  static void (*ipi_write_action)(int cpu, u32 action);
> @@ -382,11 +381,10 @@ loongson3_send_ipi_mask(const struct cpumask 
> *mask, unsigned int action)
>  		ipi_write_action(cpu_logical_map(i), (u32)action);
>  }
> 
> -
>  static irqreturn_t loongson3_ipi_interrupt(int irq, void *dev_id)
>  {
> -	int i, cpu = smp_processor_id();
> -	unsigned int action, c0count;
> +	int cpu = smp_processor_id();
> +	unsigned int action;
> 
>  	action = ipi_read_clear(cpu);
> 
> @@ -399,26 +397,14 @@ static irqreturn_t loongson3_ipi_interrupt(int 
> irq, void *dev_id)
>  		irq_exit();
>  	}
> 
> -	if (action & SMP_ASK_C0COUNT) {
> -		BUG_ON(cpu != 0);
> -		c0count = read_c0_count();
> -		c0count = c0count ? c0count : 1;
> -		for (i = 1; i < nr_cpu_ids; i++)
> -			core0_c0count[i] = c0count;
> -		nudge_writes(); /* Let others see the result ASAP */
> -	}
> -
>  	return IRQ_HANDLED;
>  }
> 
> -#define MAX_LOOPS 800
>  /*
>   * SMP init and finish on secondary CPUs
>   */
>  static void loongson3_init_secondary(void)
>  {
> -	int i;
> -	uint32_t initcount;
>  	unsigned int cpu = smp_processor_id();
>  	unsigned int imask = STATUSF_IP7 | STATUSF_IP6 |
>  			     STATUSF_IP3 | STATUSF_IP2;
> @@ -432,23 +418,6 @@ static void loongson3_init_secondary(void)
>  		     cpu_logical_map(cpu) % loongson_sysconf.cores_per_package);
>  	cpu_data[cpu].package =
>  		cpu_logical_map(cpu) / loongson_sysconf.cores_per_package;
> -
> -	i = 0;
> -	core0_c0count[cpu] = 0;
> -	loongson3_send_ipi_single(0, SMP_ASK_C0COUNT);
> -	while (!core0_c0count[cpu]) {
> -		i++;
> -		cpu_relax();
> -	}
> -
> -	if (i > MAX_LOOPS)
> -		i = MAX_LOOPS;
> -	if (cpu_data[cpu].package)
> -		initcount = core0_c0count[cpu] + i;
> -	else /* Local access is faster for loops */
> -		initcount = core0_c0count[cpu] + i/2;
> -
> -	write_c0_count(initcount);
>  }
> 
>  static void loongson3_smp_finish(void)
>
> ---
> base-commit: 0b58e108042b0ed28a71cd7edf5175999955b233
> change-id: 20240714-loongson64-cevt-r4k-eb74d4ad984c
>
> Best regards,
> -- 
> Jiaxun Yang <jiaxun.yang@...goat.com>

-- 
- Jiaxun