From: "hch@lst.de" <hch@lst.de>
To: "Michael Kelley (LINUX)" <mikelley@microsoft.com>
Cc: Robin Murphy <robin.murphy@arm.com>,
Tianyu Lan <ltykernel@gmail.com>,
KY Srinivasan <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
"wei.liu@kernel.org" <wei.liu@kernel.org>,
Dexuan Cui <decui@microsoft.com>,
"jejb@linux.ibm.com" <jejb@linux.ibm.com>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"hch@infradead.org" <hch@infradead.org>,
"m.szyprowski@samsung.com" <m.szyprowski@samsung.com>,
Tianyu Lan <Tianyu.Lan@microsoft.com>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
vkuznets <vkuznets@redhat.com>,
"konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
"hch@lst.de" <hch@lst.de>,
"parri.andrea@gmail.com" <parri.andrea@gmail.com>,
"thomas.lendacky@amd.com" <thomas.lendacky@amd.com>
Subject: Re: [PATCH] swiotlb: Max mapping size takes min align mask into account
Date: Wed, 11 May 2022 08:02:12 +0200 [thread overview]
Message-ID: <20220511060212.GA32192@lst.de> (raw)
In-Reply-To: <PH0PR21MB302530B081D6CE6470D5F9A4D7C99@PH0PR21MB3025.namprd21.prod.outlook.com>
On Tue, May 10, 2022 at 06:26:55PM +0000, Michael Kelley (LINUX) wrote:
> > Hmm, this seems a bit pessimistic - the offset can vary per mapping, so
> > it feels to me like it should really be the caller's responsibility to
> > account for it if they're already involved enough to care about both
> > constraints. But I'm not sure how practical that would be.
>
> Tianyu and I discussed this prior to his submitting the patch.
> Presumably dma_max_mapping_size() exists so that the higher
> level blk-mq code can limit the size of I/O requests to something
> that will "fit" in the swiotlb when bounce buffering is enabled.
Yes, the idea that upper level code doesn't need to care was very
much the idea behind dma_max_mapping_size().
> As you mentioned, how else would a caller handle this situation?
Well, we could look at dma_get_min_align_mask in the caller and do
the calculation there, but I really don't think that is a good idea.
So this patch looks sensible to me.
WARNING: multiple messages have this Message-ID (diff)
From: "hch@lst.de" <hch@lst.de>
To: "Michael Kelley (LINUX)" <mikelley@microsoft.com>
Cc: "parri.andrea@gmail.com" <parri.andrea@gmail.com>,
"thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
"wei.liu@kernel.org" <wei.liu@kernel.org>,
Stephen Hemminger <sthemmin@microsoft.com>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"konrad.wilk@oracle.com" <konrad.wilk@oracle.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Dexuan Cui <decui@microsoft.com>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
Tianyu Lan <ltykernel@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"hch@infradead.org" <hch@infradead.org>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>, "hch@lst.de" <hch@lst.de>,
Tianyu Lan <Tianyu.Lan@microsoft.com>,
vkuznets <vkuznets@redhat.com>, KY Srinivasan <kys@microsoft.com>,
Robin Murphy <robin.murphy@arm.com>,
"jejb@linux.ibm.com" <jejb@linux.ibm.com>
Subject: Re: [PATCH] swiotlb: Max mapping size takes min align mask into account
Date: Wed, 11 May 2022 08:02:12 +0200 [thread overview]
Message-ID: <20220511060212.GA32192@lst.de> (raw)
In-Reply-To: <PH0PR21MB302530B081D6CE6470D5F9A4D7C99@PH0PR21MB3025.namprd21.prod.outlook.com>
On Tue, May 10, 2022 at 06:26:55PM +0000, Michael Kelley (LINUX) wrote:
> > Hmm, this seems a bit pessimistic - the offset can vary per mapping, so
> > it feels to me like it should really be the caller's responsibility to
> > account for it if they're already involved enough to care about both
> > constraints. But I'm not sure how practical that would be.
>
> Tianyu and I discussed this prior to his submitting the patch.
> Presumably dma_max_mapping_size() exists so that the higher
> level blk-mq code can limit the size of I/O requests to something
> that will "fit" in the swiotlb when bounce buffering is enabled.
Yes, the idea that upper level code doesn't need to care was very
much the idea behind dma_max_mapping_size().
> As you mentioned, how else would a caller handle this situation?
Well, we could look at dma_get_min_align_mask in the caller and do
the calculation there, but I really don't think that is a good idea.
So this patch looks sensible to me.
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2022-05-11 6:02 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 14:21 [PATCH] swiotlb: Max mapping size takes min align mask into account Tianyu Lan
2022-05-10 14:21 ` Tianyu Lan
2022-05-10 16:33 ` Robin Murphy
2022-05-10 16:33 ` Robin Murphy
2022-05-10 18:26 ` Michael Kelley (LINUX)
2022-05-10 18:26 ` Michael Kelley (LINUX) via iommu
2022-05-11 6:02 ` hch [this message]
2022-05-11 6:02 ` hch
2022-05-17 9:22 ` Christoph Hellwig
2022-05-17 9:22 ` Christoph Hellwig
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