From: David Laight <david.laight.linux@gmail.com>
To: Yang Shi <yang@os.amperecomputing.com>
Cc: Heiko Carstens <hca@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Sven Schnelle <svens@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Juergen Christ <jchrist@linux.ibm.com>,
"Christoph Lameter (Ampere)" <cl@gentwo.org>,
Peter Zijlstra <peterz@infradead.org>,
Shrikanth Hegde <sshegde@linux.ibm.com>,
linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org
Subject: Re: [PATCH v3 0/9] s390: Improve this_cpu operations
Date: Thu, 21 May 2026 11:23:25 +0100 [thread overview]
Message-ID: <20260521112325.230959c9@pumpkin> (raw)
In-Reply-To: <d8e61923-2e0b-422c-b2f6-5ccedf3852bb@os.amperecomputing.com>
On Wed, 20 May 2026 17:23:37 -0700
Yang Shi <yang@os.amperecomputing.com> wrote:
> On 5/20/26 3:34 PM, David Laight wrote:
..
> >> So it seems have more overhead than the percpu page table approach IIUC.
> >> We don't need all the steps with percpu page table. And there is no
> >> penalty for migration.
> > This code looks like it relies on 'page zero' already being percpu.
> > So it probably isn't really that different.
> > Some values like the 'preemption disable count' and 'current' could be
> > (maybe are?) written into page zero to give fast access.
>
> I don't quite get what you mean about 'page zero'.
'page zero' is (at least for some cpu) the memory that can be accessed
using a small offset embedded in the instruction.
This is equivalent to using offsets from an 'always zero' %r0.
The code relies on the accesses to 960(%r0) being per-cpu.
-- David
next prev parent reply other threads:[~2026-05-21 10:23 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-20 9:22 [PATCH v3 0/9] s390: Improve this_cpu operations Heiko Carstens
2026-05-20 9:22 ` [PATCH v3 1/9] s390/alternatives: Add new ALT_TYPE_PERCPU type Heiko Carstens
2026-05-20 12:43 ` David Laight
2026-05-20 13:50 ` Heiko Carstens
2026-05-20 14:16 ` Heiko Carstens
2026-05-20 9:22 ` [PATCH v3 2/9] s390/percpu: Infrastructure for more efficient this_cpu operations Heiko Carstens
2026-05-20 9:22 ` [PATCH v3 3/9] s390/percpu: Add missing do { } while (0) constructs Heiko Carstens
2026-05-20 9:22 ` [PATCH v3 4/9] s390/percpu: Use new percpu code section for arch_this_cpu_add() Heiko Carstens
2026-05-20 9:22 ` [PATCH v3 5/9] s390/percpu: Use new percpu code section for arch_this_cpu_add_return() Heiko Carstens
2026-05-20 9:22 ` [PATCH v3 6/9] s390/percpu: Use new percpu code section for arch_this_cpu_[and|or]() Heiko Carstens
2026-05-20 9:22 ` [PATCH v3 7/9] s390/percpu: Provide arch_this_cpu_read() implementation Heiko Carstens
2026-05-20 9:22 ` [PATCH v3 8/9] s390/percpu: Provide arch_this_cpu_write() implementation Heiko Carstens
2026-05-20 9:22 ` [PATCH v3 9/9] s390/percpu: Remove one and two byte this_cpu operation implementation Heiko Carstens
2026-05-20 18:42 ` [PATCH v3 0/9] s390: Improve this_cpu operations Yang Shi
2026-05-20 22:34 ` David Laight
2026-05-21 0:23 ` Yang Shi
2026-05-21 10:17 ` David Laight
2026-05-21 16:57 ` Yang Shi
2026-05-21 17:55 ` David Laight
2026-05-21 20:46 ` Yang Shi
2026-05-21 22:13 ` David Laight
2026-05-21 23:41 ` Yang Shi
2026-05-21 10:23 ` David Laight [this message]
2026-05-21 17:48 ` Yang Shi
2026-05-21 10:37 ` Heiko Carstens
2026-05-21 17:47 ` Yang Shi
2026-05-22 9:18 ` Heiko Carstens
2026-05-27 19:09 ` Christoph Lameter (Ampere)
2026-05-27 20:38 ` Yang Shi
2026-05-28 8:36 ` David Laight
2026-05-27 23:44 ` Yang Shi
2026-05-28 9:03 ` David Laight
2026-05-28 19:19 ` Yang Shi
2026-05-28 20:34 ` David Laight
2026-05-28 14:14 ` Heiko Carstens
2026-05-28 17:14 ` David Laight
2026-05-28 18:39 ` Yang Shi
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