linux-kernel - Re: [PATCH 22/34] AMD IOMMU: add domain allocation and deallocation functions

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Message-ID: <20080710125439.GO14977@amd.com>
Date:	Thu, 10 Jul 2008 14:54:39 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	tglx@...utronix.de, mingo@...hat.com, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org, bhavna.sarathy@....com,
	Sebastian.Biemueller@....com, robert.richter@....com,
	joro@...tes.org
Subject: Re: [PATCH 22/34] AMD IOMMU: add domain allocation and deallocation functions

On Wed, Jul 09, 2008 at 07:14:59PM -0700, Andrew Morton wrote:
> On Thu, 26 Jun 2008 21:27:58 +0200 Joerg Roedel <joerg.roedel@....com> wrote:
> 
> > +static u16 domain_id_alloc(void)
> > +{
> > +	unsigned long flags;
> > +	int id;
> > +
> > +	write_lock_irqsave(&amd_iommu_devtable_lock, flags);
> > +	id = find_first_zero_bit(amd_iommu_pd_alloc_bitmap, MAX_DOMAIN_ID);
> > +	BUG_ON(id == 0);
> > +	if (id > 0 && id < MAX_DOMAIN_ID)
> > +		__set_bit(id, amd_iommu_pd_alloc_bitmap);
> > +	else
> > +		id = 0;
> > +	write_unlock_irqrestore(&amd_iommu_devtable_lock, flags);
> > +
> > +	return id;
> > +}
> 
> Presumably this is not performance-critical.  If it is, an IDR
> tree would help.

No, its not performance critical. Domain id allocation is only done at
IOMMU initialization currently. In the future it may also be used at
virtual machine creation when we have device passthrough for KVM.

Joerg

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