linux-kernel - Re: [RFC v2 0/4] futex2: Add new futex interface

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Message-ID: <4d9163924224d4265c280fc2ca6481c3@natalenko.name>
Date:   Fri, 10 Jul 2020 15:23:17 +0200
From:   Oleksandr Natalenko <oleksandr@...alenko.name>
To:     André Almeida <andrealmeid@...labora.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        peterz@...radead.org, krisman@...labora.com, kernel@...labora.com,
        dvhart@...radead.org, mingo@...hat.com,
        pgriffais@...vesoftware.com, fweimer@...hat.com,
        libc-alpha@...rceware.org, malteskarupke@....de,
        linux-api@...r.kernel.org, arnd@...db.de
Subject: Re: [RFC v2 0/4] futex2: Add new futex interface

Hello.

On 09.07.2020 19:59, André Almeida wrote:
> This RFC is a followup to the previous discussion initiated from my 
> last
> patch "futex: Implement mechanism to wait on any of several 
> futexes"[1].
> As stated in the thread, the correct approach to move forward with the
> wait multiple operation would be to create a new syscall that would 
> have
> all new cool features.
> 
> The first patch adds the new interface and just translate the call for
> the old interface, without implementing new features. The goal here is
> to establish the interface and to check if everyone is happy with this
> API. The rest of patches are selftests to show the interface in action.
> I have the following questions:
> 
> - What suggestions do you have to implement this? Start from scratch or
>   reuse the most code possible?
> 
> - The interface seems correct and implements the requirements asked by 
> you?
> 
> Those are the cool new features that this syscall should address some
> day:
> 
> - Operate with variable bit size futexes, not restricted to 32:
>   8, 16 and 64
> 
> - Wait on multiple futexes, using the following semantics:
> 
>   struct futex_wait {
> 	void *uaddr;
> 	unsigned long val;
> 	unsigned long flags;
>   };
> 
>   sys_futex_waitv(struct futex_wait *waiters, unsigned int nr_waiters,
> 		  unsigned long flags, struct __kernel_timespec *timo);
> 
> - Have NUMA optimizations: if FUTEX_NUMA_FLAG is set, the `void *uaddr`
>   argument won't be a value of type u{8, 16, 32, 64} anymore, but a 
> struct
>   containing a NUMA node hint:
> 
>   struct futex32_numa {
> 	  u32 value __attribute__ ((aligned (8)));
> 	  u32 hint;
>   };
> 
>   struct futex64_numa {
> 	  u64 value __attribute__ ((aligned (16)));
> 	  u64 hint;
>   };
> 
> Thanks,
> 	André
> 
> Changes since v1:
>  - The timeout argument now uses __kernel_timespec as type
>  - time32 interface was removed
>  v1: https://lore.kernel.org/patchwork/cover/1255437/
> 
> [1] https://lore.kernel.org/patchwork/patch/1194339/
> 
> André Almeida (4):
>   futex2: Add new futex interface
>   selftests: futex: Add futex2 wake/wait test
>   selftests: futex: Add futex2 timeout test
>   selftests: futex: Add futex2 wouldblock test
> 
>  MAINTAINERS                                   |   2 +-
>  arch/x86/entry/syscalls/syscall_32.tbl        |   2 +
>  arch/x86/entry/syscalls/syscall_64.tbl        |   2 +
>  include/linux/syscalls.h                      |   7 ++
>  include/uapi/asm-generic/unistd.h             |   8 +-
>  include/uapi/linux/futex.h                    |  10 ++
>  init/Kconfig                                  |   7 ++
>  kernel/Makefile                               |   1 +
>  kernel/futex2.c                               |  73 ++++++++++++
>  kernel/sys_ni.c                               |   4 +
>  tools/include/uapi/asm-generic/unistd.h       |   7 +-
>  .../selftests/futex/functional/.gitignore     |   1 +
>  .../selftests/futex/functional/Makefile       |   4 +-
>  .../selftests/futex/functional/futex2_wait.c  | 111 ++++++++++++++++++
>  .../futex/functional/futex_wait_timeout.c     |  38 ++++--
>  .../futex/functional/futex_wait_wouldblock.c  |  33 +++++-
>  .../testing/selftests/futex/functional/run.sh |   3 +
>  .../selftests/futex/include/futex2test.h      |  77 ++++++++++++
>  18 files changed, 373 insertions(+), 17 deletions(-)
>  create mode 100644 kernel/futex2.c
>  create mode 100644 
> tools/testing/selftests/futex/functional/futex2_wait.c
>  create mode 100644 tools/testing/selftests/futex/include/futex2test.h

What branch/tag this submission is based on please? It seems it is not a 
5.8 but rather 5.7 since the second patch misses faccessat2() syscall 
and fails to be applied cleanly.

Thanks.

-- 
   Oleksandr Natalenko (post-factum)