From: Peter Zijlstra <peterz@infradead.org>
To: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: "Arnd Bergmann" <arnd@arndb.de>,
"Thomas Gleixner" <tglx@kernel.org>,
"Ingo Molnar" <mingo@redhat.com>,
"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
"Borislav Petkov" <bp@alien8.de>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
x86@kernel.org, "Catalin Marinas" <catalin.marinas@arm.com>,
"Will Deacon" <will@kernel.org>, "Paul Walmsley" <pjw@kernel.org>,
"Palmer Dabbelt" <palmer@dabbelt.com>,
"Albert Ou" <aou@eecs.berkeley.edu>,
"Heiko Carstens" <hca@linux.ibm.com>,
"Vasily Gorbik" <gor@linux.ibm.com>,
"Alexander Gordeev" <agordeev@linux.ibm.com>,
"Darren Hart" <dvhart@infradead.org>,
"Davidlohr Bueso" <dave@stgolabs.net>,
"André Almeida" <andrealmeid@igalia.com>,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
"Samuel Holland" <samuel.holland@sifive.com>,
"Charlie Jenkins" <thecharlesjenkins@gmail.com>,
linux-arm-kernel@lists.infradead.org,
linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org,
"H. Peter Anvin" <hpa@zytor.com>,
"Thomas Huth" <thuth@redhat.com>,
"Sean Christopherson" <seanjc@google.com>,
"Jisheng Zhang" <jszhang@kernel.org>,
"Alexandre Ghiti" <alex@ghiti.fr>,
"Christian Borntraeger" <borntraeger@linux.ibm.com>,
"Sven Schnelle" <svens@linux.ibm.com>
Subject: Re: [PATCH v5 8/8] futex: Use runtime constants for __futex_hash() hot path
Date: Wed, 1 Jul 2026 09:57:14 +0200 [thread overview]
Message-ID: <20260701075714.GP48970@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20260630045531.3939-9-kprateek.nayak@amd.com>
On Tue, Jun 30, 2026 at 04:55:31AM +0000, K Prateek Nayak wrote:
> From: Peter Zijlstra <peterz@infradead.org>
>
> Runtime constify the read-only after init data __futex_shift(shift_32),
> __futex_mask(mask_32), and __futex_queues(ptr) used in __futex_hash()
> hot path to avoid referencing global variable.
>
> This also allows __futex_queues to be allocated dynamically to
> "nr_node_ids" slots instead of reserving config dependent MAX_NUMNODES
> (1 << CONFIG_NODES_SHIFT) worth of slots upfront.
>
> Runtime constants are initialized before their first access and
> runtime_const_init() provides necessary barrier to ensure subsequent
> accesses are not reordered against their initialization.
>
> No functional changes intended.
>
> [ prateek: Dynamically allocate __futex_queues, mark the global data
> __ro_after_init since they are constified after futex_init(). ]
>
> Link: https://patch.msgid.link/20260227161841.GH606826@noisy.programming.kicks-ass.net
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> # MAX_NUMNODES bloat
> Not-yet-signed-off-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
The big $1M question: does it actually make it go faster? The whole
point here was performance, right? But I'm not seeing numbers showing
how awesome these patches are.
next prev parent reply other threads:[~2026-07-01 7:57 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-30 4:55 [PATCH v5 0/8] futex: Use runtime constants for futex_hash computation K Prateek Nayak
2026-06-30 4:55 ` [PATCH v5 1/8] x86/runtime-const: Introduce runtime_const_mask_32() K Prateek Nayak
2026-06-30 4:55 ` [PATCH v5 2/8] arm64/runtime-const: Use aarch64_insn_patch_text_nosync() for patching K Prateek Nayak
2026-06-30 4:55 ` [PATCH v5 3/8] arm64/runtime-const: Introduce runtime_const_mask_32() K Prateek Nayak
2026-06-30 4:55 ` [PATCH v5 4/8] riscv/runtime-const: Replace open-coded placeholder with RUNTIME_MAGIC K Prateek Nayak
2026-06-30 6:47 ` Guo Ren
2026-06-30 4:55 ` [PATCH v5 5/8] riscv/runtime-const: Introduce runtime_const_mask_32() K Prateek Nayak
2026-06-30 4:55 ` [PATCH v5 6/8] s390/runtime-const: " K Prateek Nayak
2026-06-30 4:55 ` [PATCH v5 7/8] asm-generic/runtime-const: Add dummy runtime_const_mask_32() K Prateek Nayak
2026-06-30 4:55 ` [PATCH v5 8/8] futex: Use runtime constants for __futex_hash() hot path K Prateek Nayak
2026-07-01 7:57 ` Peter Zijlstra [this message]
2026-07-01 8:41 ` Sebastian Andrzej Siewior
2026-07-01 9:07 ` K Prateek Nayak
2026-07-01 16:17 ` [PATCH] futex: Optimise the size check get_futex_key() Sebastian Andrzej Siewior
2026-07-01 11:01 ` [PATCH v5 8/8] futex: Use runtime constants for __futex_hash() hot path Sebastian Andrzej Siewior
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