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

From: Yongji Xie <xieyongji@bytedance.com>
To: John Garry <john.garry@huawei.com>
Cc: "Will Deacon" <will@kernel.org>,
	"Michael S. Tsirkin" <mst@redhat.com>, kvm <kvm@vger.kernel.org>,
	"Jason Wang" <jasowang@redhat.com>,
	virtualization <virtualization@lists.linux-foundation.org>,
	"Christian Brauner" <christian.brauner@canonical.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Dan Carpenter" <dan.carpenter@oracle.com>,
	"Stefano Garzarella" <sgarzare@redhat.com>,
	"Liu Xiaodong" <xiaodong.liu@intel.com>,
	linux-fsdevel@vger.kernel.org,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	songmuchun@bytedance.com, "Jens Axboe" <axboe@kernel.dk>,
	"He Zhe" <zhe.he@windriver.com>,
	"Greg KH" <gregkh@linuxfoundation.org>,
	"Randy Dunlap" <rdunlap@infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	iommu@lists.linux-foundation.org, bcrl@kvack.org,
	netdev@vger.kernel.org, "Joe Perches" <joe@perches.com>,
	"Robin Murphy" <robin.murphy@arm.com>,
	"Mika Penttilä" <mika.penttila@nextfour.com>
Subject: Re: [PATCH v11 01/12] iova: Export alloc_iova_fast() and free_iova_fast()
Date: Wed, 25 Aug 2021 20:17:57 +0800	[thread overview]
Message-ID: <CACycT3uWyhNNK_YbfEAEhTk-V9CoxFg1tzVjJnXeKBFpkndnfg@mail.gmail.com> (raw)
In-Reply-To: <5f4eadda-5500-9bac-4368-48cfca6d0a4d@huawei.com>

On Wed, Aug 25, 2021 at 6:35 PM John Garry <john.garry@huawei.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@bytedance.com>
> >>
> >>
> >> This needs ack from iommu maintainers. Guys?
> >
> > Looks fine to me:
> >
> > Acked-by: Will Deacon <will@kernel.org>
> >
> > Will
> > _______________________________________________
> > iommu mailing list
> > iommu@lists.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