From: Barry Song <hidden> Date: 2021-02-23 00:39:25
BATCHED_UNMAP_TLB_FLUSH is used on x86 to do batched tlb shootdown by
sending one IPI to TLB flush all entries after unmapping pages rather
than sending an IPI to flush each individual entry.
On arm64, tlb shootdown is done by hardware. Flush instructions are
innershareable. The local flushes are limited to the boot (1 per CPU)
and when a task is getting a new ASID.
So marking this feature as "TODO" is not proper. ".." isn't good as
well. So this patch adds a "N/A" for this kind of features which are
not needed on some architectures.
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Barry Song <redacted>
---
Documentation/features/arch-support.txt | 1 +
Documentation/features/vm/TLB/arch-support.txt | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)
@@ -8,4 +8,5 @@ The meaning of entries in the tables is: | ok | # feature supported by the architecture |TODO| # feature not yet supported by the architecture | .. | # feature cannot be supported by the hardware+ | N/A| # feature doesn't apply to the architecture
BATCHED_UNMAP_TLB_FLUSH is used on x86 to do batched tlb shootdown by
sending one IPI to TLB flush all entries after unmapping pages rather
than sending an IPI to flush each individual entry.
On arm64, tlb shootdown is done by hardware. Flush instructions are
innershareable. The local flushes are limited to the boot (1 per CPU)
and when a task is getting a new ASID.
Is there any previous discussion around this ?
quoted hunk
So marking this feature as "TODO" is not proper. ".." isn't good as
well. So this patch adds a "N/A" for this kind of features which are
not needed on some architectures.
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Barry Song <redacted>
---
Documentation/features/arch-support.txt | 1 +
Documentation/features/vm/TLB/arch-support.txt | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)
@@ -8,4 +8,5 @@ The meaning of entries in the tables is: | ok | # feature supported by the architecture |TODO| # feature not yet supported by the architecture | .. | # feature cannot be supported by the hardware+ | N/A| # feature doesn't apply to the architecture
NA might be better here. s/doesn't apply/not applicable/ in order to match NA.
Still wondering if NA is really needed when there is already ".." ? Regardless
either way should be fine.
From: Song Bao Hua (Barry Song) <hidden> Date: 2021-02-23 06:21:02
-----Original Message-----
From: Anshuman Khandual [mailto:anshuman.khandual@arm.com]
Sent: Tuesday, February 23, 2021 7:10 PM
To: Song Bao Hua (Barry Song) <redacted>; corbet@lwn.net;
linux-doc@vger.kernel.org; akpm@linux-foundation.org; linux-mm@kvack.org
Cc: linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
linuxarm@openeuler.org; Mel Gorman [off-list ref]; Andy Lutomirski
[off-list ref]; Catalin Marinas [off-list ref]; Will Deacon
[off-list ref]
Subject: [Linuxarm] Re: [PATCH] Documentation/features: mark
BATCHED_UNMAP_TLB_FLUSH doesn't apply to ARM64
On 2/23/21 6:02 AM, Barry Song wrote:
quoted
BATCHED_UNMAP_TLB_FLUSH is used on x86 to do batched tlb shootdown by
sending one IPI to TLB flush all entries after unmapping pages rather
than sending an IPI to flush each individual entry.
On arm64, tlb shootdown is done by hardware. Flush instructions are
innershareable. The local flushes are limited to the boot (1 per CPU)
and when a task is getting a new ASID.
Is there any previous discussion around this ?
I copied the declaration of local flushes from:
"ARM64 Linux kernel is SMP-aware (no possibility to build only for UP).
Most of the flush instructions are innershareable. The local flushes are
limited to the boot (1 per CPU) and when a task is getting a new ASIC."
https://patchwork.kernel.org/project/xen-devel/patch/1461756173-10300-1-git-send-email-julien.grall@arm.com/
I am not sure if getting a new asid and the boot are the only two
cases of local flushes while I think this is probably true.
But even we find more corner cases, hardly the trend arm64 doesn't
need BATCHED_UNMAP_TLB_FLUSH will be changed.
quoted
So marking this feature as "TODO" is not proper. ".." isn't good as
well. So this patch adds a "N/A" for this kind of features which are
not needed on some architectures.
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Barry Song <redacted>
---
Documentation/features/arch-support.txt | 1 +
Documentation/features/vm/TLB/arch-support.txt | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)
@@ -8,4 +8,5 @@ The meaning of entries in the tables is: | ok | # feature supported by the architecture |TODO| # feature not yet supported by the architecture | .. | # feature cannot be supported by the hardware+ | N/A| # feature doesn't apply to the architecture
NA might be better here. s/doesn't apply/not applicable/ in order to match NA.
Still wondering if NA is really needed when there is already ".." ? Regardless
either way should be fine.
I don't think ".." is proper here. ".." means hardware doesn't support
the feature. But here it is just opposite, arm64 has the hardware
support of tlb shootdown rather than depending on a software IPI.
From: Will Deacon <will@kernel.org> Date: 2021-03-08 13:00:44
On Tue, Feb 23, 2021 at 01:32:30PM +1300, Barry Song wrote:
quoted hunk
BATCHED_UNMAP_TLB_FLUSH is used on x86 to do batched tlb shootdown by
sending one IPI to TLB flush all entries after unmapping pages rather
than sending an IPI to flush each individual entry.
On arm64, tlb shootdown is done by hardware. Flush instructions are
innershareable. The local flushes are limited to the boot (1 per CPU)
and when a task is getting a new ASID.
So marking this feature as "TODO" is not proper. ".." isn't good as
well. So this patch adds a "N/A" for this kind of features which are
not needed on some architectures.
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Barry Song <redacted>
---
Documentation/features/arch-support.txt | 1 +
Documentation/features/vm/TLB/arch-support.txt | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)
@@ -8,4 +8,5 @@ The meaning of entries in the tables is: | ok | # feature supported by the architecture |TODO| # feature not yet supported by the architecture | .. | # feature cannot be supported by the hardware+ | N/A| # feature doesn't apply to the architecture
From: Jonathan Corbet <corbet@lwn.net> Date: 2021-03-15 19:19:53
Barry Song [off-list ref] writes:
BATCHED_UNMAP_TLB_FLUSH is used on x86 to do batched tlb shootdown by
sending one IPI to TLB flush all entries after unmapping pages rather
than sending an IPI to flush each individual entry.
On arm64, tlb shootdown is done by hardware. Flush instructions are
innershareable. The local flushes are limited to the boot (1 per CPU)
and when a task is getting a new ASID.
So marking this feature as "TODO" is not proper. ".." isn't good as
well. So this patch adds a "N/A" for this kind of features which are
not needed on some architectures.
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Barry Song <redacted>
---
Documentation/features/arch-support.txt | 1 +
Documentation/features/vm/TLB/arch-support.txt | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)
This had a conflict with the c6x removal, but I fixed that up and
(finally) applied it, thanks.
jon
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