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From: Peter Zijlstra <peterz@infradead.org>
To: "André Almeida" <andrealmeid@collabora.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Darren Hart <dvhart@infradead.org>,
	linux-kernel@vger.kernel.org,
	Steven Rostedt <rostedt@goodmis.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	kernel@collabora.com, krisman@collabora.com,
	pgriffais@valvesoftware.com, z.figura12@gmail.com,
	joel@joelfernandes.org, malteskarupke@fastmail.fm,
	linux-api@vger.kernel.org, fweimer@redhat.com,
	libc-alpha@sourceware.org, linux-kselftest@vger.kernel.org,
	shuah@kernel.org, acme@kernel.org, corbet@lwn.net
Subject: Re: [RFC PATCH 01/13] futex2: Implement wait and wake functions
Date: Tue, 16 Feb 2021 10:56:14 +0100	[thread overview]
Message-ID: <YCuWvlKRXAygNQZP@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210215152404.250281-2-andrealmeid@collabora.com>

On Mon, Feb 15, 2021 at 12:23:52PM -0300, André Almeida wrote:
> Create a new set of futex syscalls known as futex2. This new interface
> is aimed to implement a more maintainable code, while removing obsolete
> features and expanding it with new functionalities.
> 
> Implements wait and wake semantics for futexes, along with the base
> infrastructure for future operations.

> +	futex_table = alloc_large_system_hash("futex2", sizeof(struct futex_bucket),
> +					      futex2_hashsize, 0,
> +					      futex2_hashsize < 256 ? HASH_SMALL : 0,
> +					      &futex_shift, NULL,
> +					      futex2_hashsize, futex2_hashsize);

So why are we implementing a whole second infrastrure and doubling the
memory footprint of all this?

Sure, futex.c is a pain in the ass, but most of that is not because of
the interface, most of it is having to deal with sharing state with
userspace and that being fundamentally unreliable.

Once you want to add {,UN}LOCK{,_PI} and robust futex support, you're
back to it being a giant rats nest of corner cases. Thinking a new
interface can solve any of that is naive.

So while I'm in favour of adding a new interface, I'm not sure I see
benefit of reimplementing the basics, sure it seems simpler now, but
that's because you've not implemented all the 'fun' stuff.

  parent reply	other threads:[~2021-02-16  9:57 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-15 15:23 [RFC PATCH 00/13] Add futex2 syscalls André Almeida
2021-02-15 15:23 ` [RFC PATCH 01/13] futex2: Implement wait and wake functions André Almeida
2021-02-15 19:59   ` Gabriel Krisman Bertazi
2021-02-18 13:29     ` André Almeida
2021-02-18 15:48       ` Gabriel Krisman Bertazi
2021-02-16  9:02   ` Peter Zijlstra
2021-02-18 20:09     ` André Almeida
2021-02-16  9:35   ` Peter Zijlstra
2021-02-16  9:56   ` Peter Zijlstra [this message]
2021-02-16 10:20     ` Sebastian Andrzej Siewior
2021-02-16 12:42       ` Peter Zijlstra
2021-02-16 22:12     ` Gabriel Krisman Bertazi
2021-02-15 15:23 ` [RFC PATCH 02/13] futex2: Add support for shared futexes André Almeida
2021-02-15 15:23 ` [RFC PATCH 03/13] futex2: Implement vectorized wait André Almeida
2021-02-15 20:03   ` Gabriel Krisman Bertazi
2021-02-15 20:06     ` Zebediah Figura
2021-02-15 20:08   ` Gabriel Krisman Bertazi
2021-02-15 15:23 ` [RFC PATCH 04/13] futex2: Implement requeue operation André Almeida
2021-02-15 15:23 ` [RFC PATCH 05/13] futex2: Add compatibility entry point for x86_x32 ABI André Almeida
2021-02-15 15:23 ` [RFC PATCH 06/13] docs: locking: futex2: Add documentation André Almeida
2021-02-16 18:34   ` Randy Dunlap
2021-02-18 19:12     ` André Almeida
2021-02-15 15:23 ` [RFC PATCH 07/13] selftests: futex2: Add wake/wait test André Almeida
2021-02-15 15:23 ` [RFC PATCH 08/13] selftests: futex2: Add timeout test André Almeida
2021-02-15 15:24 ` [RFC PATCH 09/13] selftests: futex2: Add wouldblock test André Almeida
2021-02-15 15:24 ` [RFC PATCH 10/13] selftests: futex2: Add waitv test André Almeida
2021-02-15 15:24 ` [RFC PATCH 11/13] selftests: futex2: Add requeue test André Almeida
2021-02-15 15:24 ` [RFC PATCH 12/13] perf bench: Add futex2 benchmark tests André Almeida
2021-02-15 15:24 ` [RFC PATCH 13/13] kernel: Enable waitpid() for futex2 André Almeida

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