From: Linus Torvalds <torvalds@linux-foundation.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Boqun Feng <boqun.feng@gmail.com>,
Andy Lutomirski <luto@amacapital.net>,
Dave Watson <davejwatson@fb.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-api <linux-api@vger.kernel.org>,
Paul Turner <pjt@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Russell King <linux@arm.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Andrew Hunter <ahh@google.com>, Andi Kleen <andi@firstfloor.org>,
Chris Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>,
rostedt <rostedt@goodmis.org>,
Josh Triplett <josh@joshtriplett.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7)
Date: Thu, 12 Apr 2018 13:07:15 -0700 [thread overview]
Message-ID: <CA+55aFwFUeNA6_0a1MOU-7VGzCw5T99cfVCPiyTpZQJdd6z=bw@mail.gmail.com> (raw)
In-Reply-To: <1580648199.9463.1523563167045.JavaMail.zimbra@efficios.com>
On Thu, Apr 12, 2018 at 12:59 PM, Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
>
> What are your concerns about page pinning ?
Pretty much everything.
It's the most complex part by far, and the vmalloc space is a limited
resource on 32-bit architectures.
> Do you have an alternative approach in mind ?
Do everything in user space.
And even if you absolutely want cpu_opv at all, why not do it in the
user space *mapping* without the aliasing into kernel space?
The cpu_opv approach isn't even fast. It's *really* slow if it has to
do VM crap.
The whole rseq thing was billed as "faster than atomics". I
*guarantee* that the cpu_opv's aren't faster than atomics.
Linus
WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Boqun Feng <boqun.feng@gmail.com>,
Andy Lutomirski <luto@amacapital.net>,
Dave Watson <davejwatson@fb.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-api <linux-api@vger.kernel.org>,
Paul Turner <pjt@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Russell King <linux@arm.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Andrew Hunter <ahh@google.com>, Andi Kleen <andi@firstfloor.org>,
Chris Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>,
rostedt <rostedt@goodmis.org>,
Josh Triplett <josh@joshtriplett.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@a>
Subject: Re: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7)
Date: Thu, 12 Apr 2018 13:07:15 -0700 [thread overview]
Message-ID: <CA+55aFwFUeNA6_0a1MOU-7VGzCw5T99cfVCPiyTpZQJdd6z=bw@mail.gmail.com> (raw)
In-Reply-To: <1580648199.9463.1523563167045.JavaMail.zimbra@efficios.com>
On Thu, Apr 12, 2018 at 12:59 PM, Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
>
> What are your concerns about page pinning ?
Pretty much everything.
It's the most complex part by far, and the vmalloc space is a limited
resource on 32-bit architectures.
> Do you have an alternative approach in mind ?
Do everything in user space.
And even if you absolutely want cpu_opv at all, why not do it in the
user space *mapping* without the aliasing into kernel space?
The cpu_opv approach isn't even fast. It's *really* slow if it has to
do VM crap.
The whole rseq thing was billed as "faster than atomics". I
*guarantee* that the cpu_opv's aren't faster than atomics.
Linus
next prev parent reply other threads:[~2018-04-12 20:07 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-12 19:27 [RFC PATCH for 4.18 00/23] Restartable sequences and CPU op vector Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 01/23] uapi headers: Provide types_32_64.h (v2) Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 02/23] rseq: Introduce restartable sequences system call (v13) Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 03/23] arm: Add restartable sequences support Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 04/23] arm: Wire up restartable sequences system call Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 05/23] x86: Add support for restartable sequences (v2) Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 06/23] x86: Wire up restartable sequence system call Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 07/23] powerpc: Add support for restartable sequences Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 08/23] powerpc: Wire up restartable sequences system call Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 09/23] sched: Implement push_task_to_cpu (v2) Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 10/23] mm: Introduce vm_map_user_ram, vm_unmap_user_ram Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 11/23] mm: Provide is_vma_noncached Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7) Mathieu Desnoyers
2018-04-12 19:43 ` Linus Torvalds
2018-04-12 19:43 ` Linus Torvalds
2018-04-12 19:59 ` Mathieu Desnoyers
2018-04-12 19:59 ` Mathieu Desnoyers
2018-04-12 20:07 ` Linus Torvalds [this message]
2018-04-12 20:07 ` Linus Torvalds
2018-04-13 12:16 ` Mathieu Desnoyers
2018-04-13 12:16 ` Mathieu Desnoyers
2018-04-13 16:37 ` Linus Torvalds
2018-04-13 16:37 ` Linus Torvalds
2018-04-13 18:06 ` Mathieu Desnoyers
2018-04-13 18:06 ` Mathieu Desnoyers
2018-04-12 20:23 ` Andi Kleen
2018-04-12 20:23 ` Andi Kleen
2018-04-16 16:28 ` Mathieu Desnoyers
2018-04-16 16:28 ` Mathieu Desnoyers
2018-04-16 17:02 ` Andi Kleen
2018-04-16 17:02 ` Andi Kleen
2018-04-14 22:44 ` Andy Lutomirski
2018-04-14 22:44 ` Andy Lutomirski
2018-04-16 18:35 ` Mathieu Desnoyers
2018-04-16 18:35 ` Mathieu Desnoyers
2018-04-16 18:39 ` Linus Torvalds
2018-04-16 18:39 ` Linus Torvalds
2018-04-16 19:21 ` Mathieu Desnoyers
2018-04-16 19:21 ` Mathieu Desnoyers
2018-04-16 19:26 ` Linus Torvalds
2018-04-16 19:26 ` Linus Torvalds
2018-04-16 20:58 ` Mathieu Desnoyers
2018-04-16 20:58 ` Mathieu Desnoyers
2018-05-04 14:32 ` Mathieu Desnoyers
2018-05-04 14:32 ` Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 13/23] x86: Wire up cpu_opv system call Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 14/23] powerpc: " Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 15/23] arm: " Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 16/23] selftests: lib.mk: Introduce OVERRIDE_TARGETS Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` mathieu.desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 17/23] cpu_opv: selftests: Implement selftests (v7) Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` mathieu.desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 18/23] rseq: selftests: Provide rseq library (v5) Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` mathieu.desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 19/23] rseq: selftests: Provide percpu_op API Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` mathieu.desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 20/23] rseq: selftests: Provide basic test Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` mathieu.desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 21/23] rseq: selftests: Provide basic percpu ops test Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` mathieu.desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 22/23] rseq: selftests: Provide parametrized tests Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` Mathieu Desnoyers
2018-04-12 19:27 ` mathieu.desnoyers
2018-04-12 19:28 ` [RFC PATCH for 4.18 23/23] rseq: selftests: Provide Makefile, scripts, gitignore Mathieu Desnoyers
2018-04-12 19:28 ` Mathieu Desnoyers
2018-04-12 19:28 ` Mathieu Desnoyers
2018-04-12 19:28 ` mathieu.desnoyers
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