From: Christoph Hellwig <hch@lst.de>
To: Jonathan Corbet <corbet@lwn.net>
Cc: Petr Tesarik <petrtesarik@huaweicloud.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Russell King <linux@armlinux.org.uk>,
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Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Juergen Gross <jgross@suse.com>,
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Roberto Sassu <roberto.sassu@huaweicloud.com>,
petr@tesarici.cz
Subject: Re: [PATCH v7 9/9] swiotlb: search the software IO TLB only if the device makes use of it
Date: Thu, 31 Aug 2023 14:51:09 +0200 [thread overview]
Message-ID: <20230831125109.GA11562@lst.de> (raw)
In-Reply-To: <87a5uz3ob8.fsf@meer.lwn.net>
On Wed, Aug 09, 2023 at 03:20:43PM -0600, Jonathan Corbet wrote:
> > spin_unlock_irqrestore(&dev->dma_io_tlb_lock, flags);
> >
> > - /* Pairs with smp_rmb() in swiotlb_find_pool(). */
> > - smp_wmb();
> > found:
> > + dev->dma_uses_io_tlb = true;
> > + /* Pairs with smp_rmb() in is_swiotlb_buffer() */
> > + smp_wmb();
> > +
>
> ...and here you set it if swiotlb is used.
>
> But, as far as I can tell, you don't actually *use* this field anywhere.
> What am I missing?
It's very much unused. Petr, I guess you wanted to use this in
is_swiotlb_buffer to avoid the lookup unless required. Can you send
a follow up?
prev parent reply other threads:[~2023-08-31 12:51 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1690871004.git.petr.tesarik.ext@huawei.com>
2023-08-01 6:38 ` [PATCH v7 0/9] Allow dynamic allocation of software IO TLB bounce buffers Greg Kroah-Hartman
2023-08-01 16:03 ` Christoph Hellwig
[not found] ` <adea71bd1fa8660d4c3157a562431ad8127016d4.1690871004.git.petr.tesarik.ext@huawei.com>
2023-08-09 21:20 ` [PATCH v7 9/9] swiotlb: search the software IO TLB only if the device makes use of it Jonathan Corbet
2023-08-30 14:55 ` Jonathan Corbet
2023-09-07 11:12 ` Petr Tesařík
2023-09-08 8:00 ` Christoph Hellwig
2023-08-31 12:51 ` Christoph Hellwig [this message]
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