Re: [PATCH 3/6] riscv: optimize send_ipi_single

From: Atish Patra <Atish.Patra@wdc.com>
To: "hch@lst.de" <hch@lst.de>,
	"paul.walmsley@sifive.com" <paul.walmsley@sifive.com>,
	"palmer@sifive.com" <palmer@sifive.com>
Cc: "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>
Subject: Re: [PATCH 3/6] riscv: optimize send_ipi_single
Date: Sat, 24 Aug 2019 00:26:26 +0000	[thread overview]
Message-ID: <570f358ed76092a4072b5acedd4ddb34c318ff9b.camel@wdc.com> (raw)
In-Reply-To: <20190821145837.3686-4-hch@lst.de>

On Wed, 2019-08-21 at 23:58 +0900, Christoph Hellwig wrote:
> Don't go through send_ipi_mask, but just set the op bit an then pass
> a
> simple generate hartid mask directly to sbi_send_ipi.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  arch/riscv/kernel/smp.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c
> index 2e21669aa068..a3715d621f60 100644
> --- a/arch/riscv/kernel/smp.c
> +++ b/arch/riscv/kernel/smp.c
> @@ -94,7 +94,13 @@ static void send_ipi_mask(const struct cpumask
> *mask, enum ipi_message_type op)
>  
>  static void send_ipi_single(int cpu, enum ipi_message_type op)
>  {
> -	send_ipi_mask(cpumask_of(cpu), op);
> +	int hartid = cpuid_to_hartid_map(cpu);
> +
> +	smp_mb__before_atomic();
> +	set_bit(op, &ipi_data[cpu].bits);
> +	smp_mb__after_atomic();
> +
> +	sbi_send_ipi(cpumask_bits(cpumask_of(hartid)));

The only cost save I see is you don't have to cpumask_clear anymore.
Is there any other cost save ? If not is it worth duplicating the code
?

May be I am being too pedantic here.. :) :)

>  }
>  
>  static inline void clear_ipi(void)

-- 
Regards,
Atish
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