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Re: [PATCH v4 8/8] swiotlb: search the software IO TLB only if a device makes use of it
- To: Petr Tesařík <petr@xxxxxxxxxxx>
- From: Christoph Hellwig <hch@xxxxxx>
- Date: Thu, 20 Jul 2023 10:22:42 +0200
- Cc: Christoph Hellwig <hch@xxxxxx>, Petr Tesarik <petrtesarik@xxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Russell King <linux@xxxxxxxxxxxxxxx>, Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>, "Rafael J. Wysocki" <rafael@xxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>, Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>, Robin Murphy <robin.murphy@xxxxxxx>, Petr Tesarik <petr.tesarik.ext@xxxxxxxxxx>, Jonathan Corbet <corbet@xxxxxxx>, Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>, Hans de Goede <hdegoede@xxxxxxxxxx>, James Seo <james@xxxxxxxxxx>, James Clark <james.clark@xxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, "moderated list:XEN HYPERVISOR ARM" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "moderated list:ARM PORT" <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>, open list <linux-kernel@xxxxxxxxxxxxxxx>, "open list:MIPS" <linux-mips@xxxxxxxxxxxxxxx>, "open list:XEN SWIOTLB SUBSYSTEM" <iommu@xxxxxxxxxxxxxxx>, Roberto Sassu <roberto.sassu@xxxxxxxxxxxxxxx>, Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
- Delivery-date: Thu, 20 Jul 2023 08:22:58 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Thu, Jul 20, 2023 at 10:02:38AM +0200, Petr Tesařík wrote:
> On Thu, 20 Jul 2023 08:47:44 +0200
> Christoph Hellwig <hch@xxxxxx> wrote:
>
> > Any reason this can't just do a list_empty_careful on the list
> > instead of adding yet another field that grows struct device?
>
> On which list?
dev->dma_io_tlb_mem->pools?
>
> The dma_io_tlb_pools list only contains transient pools, but a device
> may use bounce buffers from a regular pool.
Oh, true.
> The dma_io_tlb_mem.pools list will always be non-empty, unless the
> system runs without SWIOTLB.
>
> On a system which does have a SWIOTLB, the flag allows to differentiate
> between devices that actually use bounce buffers and devices that do
> not (e.g. because they do not have any addressing limitations).
Ok.
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