linux-kernel - Re: [RFC PATCH 1/2] swiotlb: Split up single swiotlb lock

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Message-ID: <f0ab2aa5-ca23-fa40-6147-43fc1f385bc8@arm.com>
Date:   Thu, 28 Apr 2022 15:56:24 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Tianyu Lan <ltykernel@...il.com>, m.szyprowski@...sung.com,
        michael.h.kelley@...rosoft.com, kys@...rosoft.com,
        parri.andrea@...il.com, thomas.lendacky@....com,
        wei.liu@...nel.org, Andi Kleen <ak@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        linux-hyperv@...r.kernel.org, konrad.wilk@...cle.com,
        linux-kernel@...r.kernel.org, kirill.shutemov@...el.com,
        iommu@...ts.linux-foundation.org, andi.kleen@...el.com,
        brijesh.singh@....com, vkuznets@...hat.com, hch@....de
Subject: Re: [RFC PATCH 1/2] swiotlb: Split up single swiotlb lock

On 2022-04-28 15:45, Christoph Hellwig wrote:
> On Thu, Apr 28, 2022 at 03:44:36PM +0100, Robin Murphy wrote:
>> Rather than introduce this extra level of allocator complexity, how about
>> just dividing up the initial SWIOTLB allocation into multiple io_tlb_mem
>> instances?
> 
> Yeah.  We're almost done removing all knowledge of swiotlb from drivers,
> so the very last thing I want is an interface that allows a driver to
> allocate a per-device buffer.

FWIW I'd already started thinking about having a distinct io_tlb_mem for 
non-coherent devices where vaddr is made non-cacheable to avoid the 
hassle of keeping the arch_dma_sync_* calls lined up, so I'm certainly 
in favour of bringing in a bit more flexibility at this level :)

Robin.