linux-kernel - RE: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver lowest-priority interrupts

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Message-ID: <E959C4978C3B6342920538CF579893F00C2C1C3B@SHSMSX104.ccr.corp.intel.com>
Date:	Fri, 22 Jan 2016 05:12:44 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	Radim Krcmár <rkrcmar@...hat.com>
CC:	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver
 lowest-priority interrupts



> -----Original Message-----
> From: Radim Krčmář [mailto:rkrcmar@...hat.com]
> Sent: Friday, January 22, 2016 3:50 AM
> To: Wu, Feng <feng.wu@...el.com>
> Cc: pbonzini@...hat.com; linux-kernel@...r.kernel.org;
> kvm@...r.kernel.org
> Subject: Re: [PATCH v3 2/4] KVM: x86: Use vector-hashing to deliver lowest-
> priority interrupts
> 
> 2016-01-20 09:42+0800, Feng Wu:
> > Use vector-hashing to deliver lowest-priority interrupts, As an
> > example, modern Intel CPUs in server platform use this method to
> > handle lowest-priority interrupts.
> >
> > Signed-off-by: Feng Wu <feng.wu@...el.com>
> > ---
> 
> Functionality looks good, so I had a lot of stylistic comments, sorry :)

Any comments are welcome! Thank you! :)

> 
> > +		       const unsigned long *bitmap, u32 bitmap_size)
> > +{
> > +	u32 mod;
> > +	int i, idx = 0;
> > +
> > +	mod = vector % dest_vcpus;
> > +
> > +	for (i = 0; i <= mod; i++) {
> > +		idx = find_next_bit(bitmap, bitmap_size, idx) + 1;
> 
> I'd remove this "+ 1".  Current users don't check for errors and always
> do "- 1".  The new error value could be 'idx = bitmap_size', with u32 as
> return type.
> 

Does the following code look good to you:

        u32 mod;
        int i, idx = -1;

        mod = vector % dest_vcpus;

        for (i = 0; i <= mod; i++) {
                idx = find_next_bit(bitmap, bitmap_size, idx + 1);
                BUG_ON(idx == bitmap_size);
        }

        return idx;

Thanks,
Feng