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From: David Laight <david.laight.linux@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Thomas Gleixner" <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Darren Hart" <dvhart@infradead.org>,
	"Davidlohr Bueso" <dave@stgolabs.net>,
	"André Almeida" <andrealmeid@igalia.com>,
	"kernel test robot" <lkp@intel.com>,
	"Russell King" <linux@armlinux.org.uk>,
	linux-arm-kernel@lists.infradead.org, x86@kernel.org,
	"Madhavan Srinivasan" <maddy@linux.ibm.com>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Christophe Leroy" <christophe.leroy@csgroup.eu>,
	linuxppc-dev@lists.ozlabs.org, "Paul Walmsley" <pjw@kernel.org>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	linux-riscv@lists.infradead.org,
	"Heiko Carstens" <hca@linux.ibm.com>,
	"Christian Borntraeger" <borntraeger@linux.ibm.com>,
	"Sven Schnelle" <svens@linux.ibm.com>,
	linux-s390@vger.kernel.org,
	"Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Julia Lawall" <Julia.Lawall@inria.fr>,
	"Nicolas Palix" <nicolas.palix@imag.fr>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Christian Brauner" <brauner@kernel.org>,
	"Jan Kara" <jack@suse.cz>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [patch V4 10/12] futex: Convert to scoped user access
Date: Thu, 23 Oct 2025 22:14:50 +0100	[thread overview]
Message-ID: <20251023221450.1303003d@pumpkin> (raw)
In-Reply-To: <CAHk-=wjoQvKpfB4X0ftqM0P0kzaZxor7C1JBC5PrLPY-ca=fnA@mail.gmail.com>

On Thu, 23 Oct 2025 09:26:12 -1000
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Thu, 23 Oct 2025 at 08:44, Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > But as you said out-of-line function call it occured to me that these
> > helpers might be just named get/put_user_inline(). Hmm?  
> 
> Yeah, with a comment that clearly says "you need to have actual
> performance numbers for why this needs to be inlined" for people to
> use it.

Avoiding an extra clac/stac pair for two accesses might be enough.
But for a single access it might be hard to justify.

(Even if 'return' instructions are horribly painful.
Although anyone chasing performance is probably using a local system
and just disables all that 'stuff'.)

> 
>            Linus



WARNING: multiple messages have this Message-ID (diff)
From: David Laight <david.laight.linux@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Thomas Gleixner" <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Darren Hart" <dvhart@infradead.org>,
	"Davidlohr Bueso" <dave@stgolabs.net>,
	"André Almeida" <andrealmeid@igalia.com>,
	"kernel test robot" <lkp@intel.com>,
	"Russell King" <linux@armlinux.org.uk>,
	linux-arm-kernel@lists.infradead.org, x86@kernel.org,
	"Madhavan Srinivasan" <maddy@linux.ibm.com>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Christophe Leroy" <christophe.leroy@csgroup.eu>,
	linuxppc-dev@lists.ozlabs.org, "Paul Walmsley" <pjw@kernel.org>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	linux-riscv@lists.infradead.org,
	"Heiko Carstens" <hca@linux.ibm.com>,
	"Christian Borntraeger" <borntraeger@linux.ibm.com>,
	"Sven Schnelle" <svens@linux.ibm.com>,
	linux-s390@vger.kernel.org,
	"Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Julia Lawall" <Julia.Lawall@inria.fr>,
	"Nicolas Palix" <nicolas.palix@imag.fr>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Christian Brauner" <brauner@kernel.org>,
	"Jan Kara" <jack@suse.cz>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [patch V4 10/12] futex: Convert to scoped user access
Date: Thu, 23 Oct 2025 22:14:50 +0100	[thread overview]
Message-ID: <20251023221450.1303003d@pumpkin> (raw)
In-Reply-To: <CAHk-=wjoQvKpfB4X0ftqM0P0kzaZxor7C1JBC5PrLPY-ca=fnA@mail.gmail.com>

On Thu, 23 Oct 2025 09:26:12 -1000
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Thu, 23 Oct 2025 at 08:44, Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> > But as you said out-of-line function call it occured to me that these
> > helpers might be just named get/put_user_inline(). Hmm?  
> 
> Yeah, with a comment that clearly says "you need to have actual
> performance numbers for why this needs to be inlined" for people to
> use it.

Avoiding an extra clac/stac pair for two accesses might be enough.
But for a single access it might be hard to justify.

(Even if 'return' instructions are horribly painful.
Although anyone chasing performance is probably using a local system
and just disables all that 'stuff'.)

> 
>            Linus


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

  reply	other threads:[~2025-10-23 21:15 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-10-22 12:49 [patch V4 00/12] uaccess: Provide and use scopes for user access Thomas Gleixner
2025-10-22 12:49 ` Thomas Gleixner
2025-10-22 12:49 ` [patch V4 01/12] ARM: uaccess: Implement missing __get_user_asm_dword() Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 12:49 ` [patch V4 02/12] uaccess: Provide ASM GOTO safe wrappers for unsafe_*_user() Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 12:49 ` [patch V4 03/12] x86/uaccess: Use unsafe wrappers for ASM GOTO Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 12:49 ` [patch V4 04/12] powerpc/uaccess: " Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 12:49 ` [patch V4 05/12] riscv/uaccess: " Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 12:49 ` [patch V4 06/12] s390/uaccess: " Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 15:00   ` Heiko Carstens
2025-10-22 15:00     ` Heiko Carstens
2025-10-22 12:49 ` [patch V4 07/12] uaccess: Provide scoped user access regions Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 14:20   ` David Laight
2025-10-22 14:20     ` David Laight
2025-10-22 14:23     ` Peter Zijlstra
2025-10-22 14:23       ` Peter Zijlstra
2025-10-22 12:49 ` [patch V4 08/12] uaccess: Provide put/get_user_scoped() Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 12:49 ` [patch V4 09/12] [RFC] coccinelle: misc: Add scoped_$MODE_access() checker script Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 12:49 ` [patch V4 10/12] futex: Convert to scoped user access Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 15:16   ` Linus Torvalds
2025-10-22 15:16     ` Linus Torvalds
2025-10-23 18:44     ` Thomas Gleixner
2025-10-23 18:44       ` Thomas Gleixner
2025-10-23 19:26       ` Linus Torvalds
2025-10-23 19:26         ` Linus Torvalds
2025-10-23 21:14         ` David Laight [this message]
2025-10-23 21:14           ` David Laight
2025-10-22 12:49 ` [patch V4 11/12] x86/futex: " Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 12:49 ` [patch V4 12/12] select: " Thomas Gleixner
2025-10-22 12:49   ` Thomas Gleixner
2025-10-22 13:28 ` [patch V4 00/12] uaccess: Provide and use scopes for " Peter Zijlstra
2025-10-22 13:28   ` Peter Zijlstra

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