From: Joerg Roedel <joro@8bytes.org>
To: Qian Cai <cai@lca.pw>
Cc: iommu@lists.linux-foundation.org, Joerg Roedel <jroedel@suse.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/2] iommu/amd: Don't use atomic64_t for domain->pt_root
Date: Tue, 30 Jun 2020 11:57:21 +0200 [thread overview]
Message-ID: <20200630095721.GI28824@8bytes.org> (raw)
In-Reply-To: <63D91069-6A2E-4C05-8409-76A56D1E0FCA@lca.pw>
On Fri, Jun 26, 2020 at 08:30:21AM -0400, Qian Cai wrote:
> BTW, from the previous discussion, Linus mentioned,
>
> “
> The thing is, the 64-bit atomic reads/writes are very expensive on
> 32-bit x86. If it was just a native pointer, it would be much cheaper
> than an "atomic64_t".
> “
>
> However, here we have AMD_IOMMU depend on x86_64, so I am wondering if
> it makes any sense to run this code on 32-bit x86 at all?
No, it doesn't, the driver is not supported on 32bit and probably never
will. I skip this patch and only apply the first one, as it is an
improvement in itself.
Regards,
Joerg
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WARNING: multiple messages have this Message-ID (diff)
From: Joerg Roedel <joro@8bytes.org>
To: Qian Cai <cai@lca.pw>
Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Joerg Roedel <jroedel@suse.de>
Subject: Re: [PATCH v2 0/2] iommu/amd: Don't use atomic64_t for domain->pt_root
Date: Tue, 30 Jun 2020 11:57:21 +0200 [thread overview]
Message-ID: <20200630095721.GI28824@8bytes.org> (raw)
In-Reply-To: <63D91069-6A2E-4C05-8409-76A56D1E0FCA@lca.pw>
On Fri, Jun 26, 2020 at 08:30:21AM -0400, Qian Cai wrote:
> BTW, from the previous discussion, Linus mentioned,
>
> “
> The thing is, the 64-bit atomic reads/writes are very expensive on
> 32-bit x86. If it was just a native pointer, it would be much cheaper
> than an "atomic64_t".
> “
>
> However, here we have AMD_IOMMU depend on x86_64, so I am wondering if
> it makes any sense to run this code on 32-bit x86 at all?
No, it doesn't, the driver is not supported on 32bit and probably never
will. I skip this patch and only apply the first one, as it is an
improvement in itself.
Regards,
Joerg
next prev parent reply other threads:[~2020-06-30 9:57 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-26 8:05 [PATCH v2 0/2] iommu/amd: Don't use atomic64_t for domain->pt_root Joerg Roedel
2020-06-26 8:05 ` Joerg Roedel
2020-06-26 8:05 ` [PATCH v2 1/2] iommu/amd: Add helper functions to update domain->pt_root Joerg Roedel
2020-06-26 8:05 ` Joerg Roedel
2020-06-26 8:05 ` [PATCH v2 2/2] iommu/amd: Use 'unsigned long' for domain->pt_root Joerg Roedel
2020-06-26 8:05 ` Joerg Roedel
2020-06-26 12:30 ` [PATCH v2 0/2] iommu/amd: Don't use atomic64_t " Qian Cai
2020-06-26 12:30 ` Qian Cai
2020-06-30 9:57 ` Joerg Roedel [this message]
2020-06-30 9:57 ` Joerg Roedel
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