linux-kernel - Re: [PATCH v2 2/2] x86/hyperv: remove on-stack cpumask from hv_send_ipi_mask

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Date:   Sat, 11 Sep 2021 15:24:26 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] x86/hyperv: remove on-stack cpumask from
 hv_send_ipi_mask_allbutself

On Sat, Sep 11, 2021 at 03:09:50PM +0000, Michael Kelley wrote:
> From: Wei Liu <wei.liu@...nel.org> Sent: Friday, September 10, 2021 11:57 AM
[...]
> > -static bool __send_ipi_mask(const struct cpumask *mask, int vector)
> > +static bool __send_ipi_mask(const struct cpumask *mask, int vector,
> > +		bool exclude_self)
> >  {
> > -	int cur_cpu, vcpu;
> > +	int cur_cpu, vcpu, this_cpu = smp_processor_id();
> >  	struct hv_send_ipi ipi_arg;
> >  	u64 status;
> > +	unsigned int weight;
> > 
> >  	trace_hyperv_send_ipi_mask(mask, vector);
> > 
> > -	if (cpumask_empty(mask))
> > +	weight = cpumask_weight(mask);
> > +
> > +	/*
> > +	 * Do nothing if
> > +	 *   1. the mask is empty
> > +	 *   2. the mask only contains self when exclude_self is true
> > +	 */
> > +	if (weight == 0 ||
> > +	    (exclude_self && weight == 1 && cpumask_first(mask) == this_cpu))
> 
> Nit:  cpumask_test_cpu(this_cpu, mask) would seem to be a better fit for this
> use case than cpumask_first().  But either works.

I will adjust the code when I commit this patch.

Wei.