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From:   Roman Skakun <rm.skakun@gmail.com>
Date:   Thu, 16 Sep 2021 12:40:28 +0300
Message-ID: <CADu_u-OjpYB0-B=tLKYsZH=auvQF-o7PJb-11W=1emY8jaA-mg@mail.gmail.com>
Subject: Re: [PATCH] swiotlb: set IO TLB segment size via cmdline
To:     Stefano Stabellini <sstabellini@kernel.org>
Cc:     Jan Beulich <jbeulich@suse.com>,
        Andrii Anisov <andrii_anisov@epam.com>,
        Roman Skakun <roman_skakun@epam.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Maciej W. Rozycki" <macro@orcam.me.uk>,
        Muchun Song <songmuchun@bytedance.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Mike Rapoport <rppt@kernel.org>, Will Deacon <will@kernel.org>,
        xen-devel@lists.xenproject.org, linux-mips@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        iommu <iommu@lists.linux-foundation.org>,
        Christoph Hellwig <hch@lst.de>
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Hi Stefano,

> Also, Option 1 listed in the webpage seems to be a lot better. Any
> reason you can't do that? Because that option both solves the problem
> and increases performance.

Yes, Option 1 is probably more efficient.
But I use another platform under Xen without DMA adjustment functionality.
I pinned this webpage only for example to describe the similar problem I ha=
d.

Cheers,
Roman

=D1=81=D1=80, 15 =D1=81=D0=B5=D0=BD=D1=82. 2021 =D0=B3. =D0=B2 04:51, Stefa=
no Stabellini <sstabellini@kernel.org>:

>
> On Tue, 14 Sep 2021, Christoph Hellwig wrote:
> > On Tue, Sep 14, 2021 at 05:29:07PM +0200, Jan Beulich wrote:
> > > I'm not convinced the swiotlb use describe there falls under "intende=
d
> > > use" - mapping a 1280x720 framebuffer in a single chunk? (As an aside=
,
> > > the bottom of this page is also confusing, as following "Then we can
> > > confirm the modified swiotlb size in the boot log:" there is a log
> > > fragment showing the same original size of 64Mb.
> >
> > It doesn't.  We also do not add hacks to the kernel for whacky out
> > of tree modules.
>
> Also, Option 1 listed in the webpage seems to be a lot better. Any
> reason you can't do that? Because that option both solves the problem
> and increases performance.


--
Best Regards, Roman.