From: "André Almeida" <andrealmeid@collabora.com>
To: Gabriel Krisman Bertazi <krisman@collabora.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Darren Hart <dvhart@infradead.org>,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
kernel@collabora.com, linux-api@vger.kernel.org,
libc-alpha@sourceware.org, mtk.manpages@gmail.com,
Davidlohr Bueso <dave@stgolabs.net>,
Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v3 2/6] futex2: Implement vectorized wait
Date: Tue, 14 Sep 2021 14:18:58 -0300 [thread overview]
Message-ID: <58536544-e032-1954-ce30-d131869dc95e@collabora.com> (raw)
In-Reply-To: <875yv4ge83.fsf@collabora.com>
Hi Gabriel, thanks for the feedback! A few clarifications:
Às 22:03 de 13/09/21, Gabriel Krisman Bertazi escreveu:
> André Almeida <andrealmeid@collabora.com> writes:
>
>> Add support to wait on multiple futexes. This is the interface
>> implemented by this syscall:
>>
[...]
>>
>> +/*
>> + * Flags to specify the bit length of the futex word for futex2 syscalls.
>> + * Currently, only 32 is supported.
>> + */
>> +#define FUTEX_32 2
>
> Why start at 2?
I was planning to do:
FUTEX_8 0
FUTEX_16 1
FUTEX_32 2
FUTEX_64 3
>
>> +
>> +/*
>> + * Max numbers of elements in a futex_waitv array
>> + */
>> +#define FUTEX_WAITV_MAX 128
>> +
>> +/**
>> + * struct futex_waitv - A waiter for vectorized wait
>> + * @val: Expected value at uaddr
>> + * @uaddr: User address to wait on
>> + * @flags: Flags for this waiter
>> + * @__reserved: Reserved member to preserve data alignment. Should be 0.
>> + */
>> +struct futex_waitv {
>> + __u64 val;
>> + __u64 uaddr;
>> + __u32 flags;
>> + __u32 __reserved;
>> +};
>
> why force uaddr to be __u64, even for 32-bit? uaddr could be a (void*) for
> all we care, no? Also, by adding a reserved field, you are wasting 32
> bits even on 32-bit architectures.
>
We do that to make the structure layout compatible with both entry
points, remove the need for special cast and duplicated code, as
suggested by Thomas and Arnd:
https://lore.kernel.org/lkml/87v94310gm.ffs@tglx/
https://lore.kernel.org/lkml/CAK8P3a0MO1qJLRkCH8KrZ3+=L66KOsMRmcbrUvYdMoKykdKoyQ@mail.gmail.com/
next prev parent reply other threads:[~2021-09-14 17:19 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-13 17:52 [PATCH v3 0/6] futex2: Add wait on multiple futexes syscall André Almeida
2021-09-13 17:52 ` [PATCH v3 1/6] futex: Prepare for futex_wait_multiple() André Almeida
2021-09-13 17:52 ` [PATCH v3 2/6] futex2: Implement vectorized wait André Almeida
2021-09-14 1:03 ` Gabriel Krisman Bertazi
2021-09-14 17:18 ` André Almeida [this message]
2021-09-16 4:10 ` Gabriel Krisman Bertazi
2021-09-16 11:20 ` Peter Zijlstra
2021-09-16 11:50 ` Arnd Bergmann
2021-09-16 13:37 ` Steven Rostedt
2021-09-16 16:36 ` Gabriel Krisman Bertazi
2021-09-13 17:52 ` [PATCH v3 3/6] futex2: wire up syscall for x86 André Almeida
2021-09-13 17:52 ` [PATCH v3 4/6] futex2: wire up syscall for ARM André Almeida
2021-09-13 17:52 ` [PATCH v3 5/6] selftests: futex2: Add waitv test André Almeida
2021-09-14 1:11 ` Gabriel Krisman Bertazi
2021-09-13 17:52 ` [PATCH v3 6/6] selftests: futex2: Test futex_waitv timeout André Almeida
2021-09-14 1:05 ` [PATCH v3 0/6] futex2: Add wait on multiple futexes syscall Gabriel Krisman Bertazi
2021-09-14 3:07 ` André Almeida
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