linux-kernel - RE: [RFC 1/1] swiotlb: Reduce calls to swiotlb_find

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Date: Thu, 27 Jun 2024 14:59:03 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Petr Tesařík <petr@...arici.cz>, "hch@....de"
	<hch@....de>
CC: "robin.murphy@....com" <robin.murphy@....com>, "joro@...tes.org"
	<joro@...tes.org>, "will@...nel.org" <will@...nel.org>, "jgross@...e.com"
	<jgross@...e.com>, "sstabellini@...nel.org" <sstabellini@...nel.org>,
	"oleksandr_tyshchenko@...m.com" <oleksandr_tyshchenko@...m.com>,
	"m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: RE: [RFC 1/1] swiotlb: Reduce calls to swiotlb_find_pool()

From: Petr Tesařík <petr@...arici.cz> Sent: Wednesday, June 26, 2024 11:52 PM
> 
> Oh, right. The idea is good, but I was not able to reply immediately
> and then forgot about it.
> 
> For the record, I considered an alternative: Call swiotlb_* functions
> unconditionally and bail out early if the pool is NULL. But it's no
> good, because is_swiotlb_buffer() can be inlined, so this approach
> would replace a quick check with a function call. And then there's also
> swiotlb_tbl_unmap_single()...
> 
> I have only a very minor suggestion: Could is_swiotlb_buffer() be
> renamed now that it no longer returns a bool? OTOH I have no good
> immediate idea myself.
>

Conceptually, it's still being used as a boolean function based on
whether the return value is NULL.  Renaming it to swiotlb_get_pool()
more accurately describes the return value, but obscures the
intent of determining if it is a swiotlb buffer.  I'll think about it.
Suggestions are welcome.

Michael