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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "K Prateek Nayak" <kprateek.nayak@amd.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Thomas Gleixner" <tglx@kernel.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"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 10:41:50 +0200	[thread overview]
Message-ID: <20260701084150.GNOeboLw@linutronix.de> (raw)
In-Reply-To: <20260701075714.GP48970@noisy.programming.kicks-ass.net>

On 2026-07-01 09:57:14 [+0200], Peter Zijlstra wrote:
> 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.

I did complain about the about the size of __futex_data which is blown
on distro kernels due to CONFIG_NODES_SHIFT=10 on Debian for instance.
This makes it go away at no extra price but yeah let me boot a big box
and see.
If the performance remains unchanged it is still worth considering due
to size savings on the average box with 1 node. The biggest box I have
access to has four nodes. If I remember correctly, Prateek was saying
that AMD has "normal" boxes which would require =9 for normal operation
and they do run distro kernels so lowering that value is not an option.

Sebastian

WARNING: multiple messages have this Message-ID (diff)
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "K Prateek Nayak" <kprateek.nayak@amd.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Thomas Gleixner" <tglx@kernel.org>,
	"Ingo Molnar" <mingo@redhat.com>,
	"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 10:41:50 +0200	[thread overview]
Message-ID: <20260701084150.GNOeboLw@linutronix.de> (raw)
In-Reply-To: <20260701075714.GP48970@noisy.programming.kicks-ass.net>

On 2026-07-01 09:57:14 [+0200], Peter Zijlstra wrote:
> 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.

I did complain about the about the size of __futex_data which is blown
on distro kernels due to CONFIG_NODES_SHIFT=10 on Debian for instance.
This makes it go away at no extra price but yeah let me boot a big box
and see.
If the performance remains unchanged it is still worth considering due
to size savings on the average box with 1 node. The biggest box I have
access to has four nodes. If I remember correctly, Prateek was saying
that AMD has "normal" boxes which would require =9 for normal operation
and they do run distro kernels so lowering that value is not an option.

Sebastian

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

  reply	other threads:[~2026-07-01  8:41 UTC|newest]

Thread overview: 41+ 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 ` 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   ` 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   ` 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   ` K Prateek Nayak
2026-06-30  5:07   ` sashiko-bot
2026-06-30  8:16     ` 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  4:55   ` K Prateek Nayak
2026-06-30  6:47   ` Guo Ren
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   ` K Prateek Nayak
2026-06-30  4:55 ` [PATCH v5 6/8] s390/runtime-const: " K Prateek Nayak
2026-06-30  4:55   ` 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   ` K Prateek Nayak
2026-06-30  4:55 ` [PATCH v5 8/8] futex: Use runtime constants for __futex_hash() hot path K Prateek Nayak
2026-06-30  4:55   ` K Prateek Nayak
2026-06-30  5:20   ` sashiko-bot
2026-07-01  7:57   ` Peter Zijlstra
2026-07-01  7:57     ` Peter Zijlstra
2026-07-01  8:41     ` Sebastian Andrzej Siewior [this message]
2026-07-01  8:41       ` Sebastian Andrzej Siewior
2026-07-01  9:07       ` K Prateek Nayak
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 16:17           ` Sebastian Andrzej Siewior
2026-07-02  8:59           ` Peter Zijlstra
2026-07-02  8:59             ` Peter Zijlstra
2026-07-02 10:56             ` Sebastian Andrzej Siewior
2026-07-02 10:56               ` Sebastian Andrzej Siewior
2026-07-02 11:18               ` Peter Zijlstra
2026-07-02 11:18                 ` Peter Zijlstra
2026-07-01 11:01       ` [PATCH v5 8/8] futex: Use runtime constants for __futex_hash() hot path Sebastian Andrzej Siewior
2026-07-01 11:01         ` Sebastian Andrzej Siewior
2026-07-01 19:58   ` Sebastian Andrzej Siewior
2026-07-01 19:58     ` Sebastian Andrzej Siewior

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