linux-kernel - Re: [PATCH 3/5] X86: Hyper-V: Enhanced IPI enlightenment

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Date:   Fri, 27 Apr 2018 00:16:51 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "K. Y. Srinivasan" <kys@...rosoft.com>
cc:     x86@...nel.org, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, devel@...uxdriverproject.org,
        olaf@...fle.de, apw@...onical.com, jasowang@...hat.com,
        hpa@...or.com, sthemmin@...rosoft.com,
        Michael.H.Kelley@...rosoft.com, vkuznets@...hat.com
Subject: Re: [PATCH 3/5] X86: Hyper-V: Enhanced IPI enlightenment

On Wed, 25 Apr 2018, kys@...uxonhyperv.com wrote:
>  
> +struct ipi_arg_ex {
> +	u32 vector;
> +	u32  reserved;
> +	struct hv_vpset vp_set;

Please align that in tabular fashion for easy of reading

	u32		vector;
	u32  		reserved;
	struct hv_vpset	vp_set;

> +};
> +
>  static struct apic orig_apic;
>  
>  static u64 hv_apic_icr_read(void)
> @@ -97,6 +103,40 @@ static void hv_apic_eoi_write(u32 reg, u32 val)
>   * IPI implementation on Hyper-V.
>   */
>  
> +static int __send_ipi_mask_ex(const struct cpumask *mask, int vector)
> +{
> +	int nr_bank = 0;
> +	struct ipi_arg_ex **arg;
> +	struct ipi_arg_ex *ipi_arg;
> +	int ret = 1;
> +	unsigned long flags;

This is really horrible to read.

	struct ipi_arg_ex *ipi_arg;
	struct ipi_arg_ex **arg;
	unsigned long flags;
	bool ret = false;
	int nr_bank = 0;

is really more conveniant for quick reading.

So the other more limited function has a lot more sanity checks vs. vector
number and other things. Why are they not required here? Comment please.

> +	local_irq_save(flags);
> +	arg = (struct ipi_arg_ex **)this_cpu_ptr(hyperv_pcpu_input_arg);
> +
> +	ipi_arg = *arg;
> +	if (unlikely(!ipi_arg))
> +		goto ipi_mask_ex_done;
> +
> +	ipi_arg->vector = vector;
> +	ipi_arg->reserved = 0;
> +	ipi_arg->vp_set.valid_bank_mask = 0;
> +
> +	if (!cpumask_equal(mask, cpu_present_mask)) {
> +		ipi_arg->vp_set.format = HV_GENERIC_SET_SPARCE_4K;
> +		nr_bank = cpumask_to_vpset(&(ipi_arg->vp_set), mask);

nr_bank really confused me. bank_nr is what you mean, not number of banks,
right?

> +	}
> +	if (!nr_bank)
> +		ipi_arg->vp_set.format = HV_GENERIC_SET_ALL;
> +
> +	ret = hv_do_rep_hypercall(HVCALL_SEND_IPI_EX, 0, nr_bank,
> +			      ipi_arg, NULL);
> +
> +ipi_mask_ex_done:
> +	local_irq_restore(flags);
> +	return ret;
> +}

Thanks,

	tglx