linux-kernel - Re: [PATCH v11 01/12] iova: Export alloc_iova_fast() and free_iova_fast()

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Date:   Wed, 25 Aug 2021 20:17:57 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     John Garry <john.garry@...wei.com>
Cc:     Will Deacon <will@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>, kvm <kvm@...r.kernel.org>,
        Jason Wang <jasowang@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Jonathan Corbet <corbet@....net>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Liu Xiaodong <xiaodong.liu@...el.com>,
        linux-fsdevel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        songmuchun@...edance.com, Jens Axboe <axboe@...nel.dk>,
        He Zhe <zhe.he@...driver.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, bcrl@...ck.org,
        netdev@...r.kernel.org, Joe Perches <joe@...ches.com>,
        Robin Murphy <robin.murphy@....com>,
        Mika Penttilä <mika.penttila@...tfour.com>
Subject: Re: [PATCH v11 01/12] iova: Export alloc_iova_fast() and free_iova_fast()

On Wed, Aug 25, 2021 at 6:35 PM John Garry <john.garry@...wei.com> wrote:
>
> On 25/08/2021 10:55, Will Deacon wrote:
> > On Tue, Aug 24, 2021 at 02:08:33PM -0400, Michael S. Tsirkin wrote:
> >> On Wed, Aug 18, 2021 at 08:06:31PM +0800, Xie Yongji wrote:
> >>> Export alloc_iova_fast() and free_iova_fast() so that
> >>> some modules can make use of the per-CPU cache to get
> >>> rid of rbtree spinlock in alloc_iova() and free_iova()
> >>> during IOVA allocation.
> >>>
> >>> Signed-off-by: Xie Yongji <xieyongji@...edance.com>
> >>
> >>
> >> This needs ack from iommu maintainers. Guys?
> >
> > Looks fine to me:
> >
> > Acked-by: Will Deacon <will@...nel.org>
> >
> > Will
> > _______________________________________________
> > iommu mailing list
> > iommu@...ts.linux-foundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/iommu
> > .
> >
>
> JFYI, There was a preliminary discussion to move the iova rcache code
> (which the iova fast alloc and free functions are based on) out of the
> iova code and maybe into dma-iommu (being the only user). There was
> other motivation.
>

Would it be better to move the code into ./lib as a general library?

> https://lore.kernel.org/linux-iommu/83de3911-145d-77c8-17c1-981e4ff825d3@arm.com/
>
> Having more users complicates that...
>

Do we have some plan for this work? From our test [1],
iova_alloc_fast() is much better than iova_alloc(). So I'd like to use
it as much as possible

[1] https://lore.kernel.org/kvm/CACycT3steXFeg7NRbWpo2J59dpYcumzcvM2zcPJAVe40-EvvEg@mail.gmail.com/

Thanks,
Yongji

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