From: "H.J. Lu" <hjl.tools@gmail.com>
To: "André Almeida" <andrealmeid@collabora.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Florian Weimer <fweimer@redhat.com>,
malteskarupke@web.de, GNU C Library <libc-alpha@sourceware.org>,
Linux API <linux-api@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
dvhart@infradead.org, kernel@collabora.com,
krisman@collabora.com, pgriffais@valvesoftware.com
Subject: Re: [RFC 0/4] futex2: Add new futex interface
Date: Fri, 12 Jun 2020 12:35:19 -0700 [thread overview]
Message-ID: <CAMe9rOqnBRzXv4xnhFvOgdVpDo0oRc1SYq38zcJWo9BPZseagg@mail.gmail.com> (raw)
In-Reply-To: <20200612185122.327860-1-andrealmeid@collabora.com>
On Fri, Jun 12, 2020 at 11:53 AM André Almeida via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> Hello,
>
> 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:
>
> - Has anyone stared worked on a implementation of this interface? If
> yes, it would be nice to share the progress so we don't have duplicated
> work.
>
> - 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?
>
> - The proposed interface uses ktime_t type for absolute timeout, and I
> assumed that it should use values in a nsec resolution. If this is true,
> we have some problems with i386 ABI, please check out the
> COMPAT_32BIT_TIME implementation in patch 1 for more details. I
> haven't added a time64 implementation yet, until this is clarified.
>
> - Is expected to have a x32 ABI implementation as well? In the case of
> wait and wake, we could use the same as x86_64 ABI. However, for the
> waitv (aka wait on multiple futexes) we would need a proper x32 entry
> since we are dealing with 32bit pointers.
x32 should be able to use the same i386 compat systcall entry. Will it be
problem?
> 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, ktime_t *timo);
>
> - Have NUMA optimizations: if FUTEX_NUMA_FLAG is present, the `void *uaddr`
> argument won't be a u{8, 16, 32, 64} value 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;
> };
>
H.J.
next prev parent reply other threads:[~2020-06-12 19:35 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-12 18:51 [RFC 0/4] futex2: Add new futex interface André Almeida
2020-06-12 18:51 ` [RFC 1/4] " André Almeida
2020-06-12 18:51 ` [RFC 2/4] selftests: futex: Add futex2 wake/wait test André Almeida
2020-06-12 18:51 ` [RFC 3/4] selftests: futex: Add futex2 timeout test André Almeida
2020-06-12 18:51 ` [RFC 4/4] selftests: futex: Add futex2 wouldblock test André Almeida
2020-06-12 19:35 ` H.J. Lu [this message]
2020-06-13 19:25 ` [RFC 0/4] futex2: Add new futex interface André Almeida
2020-06-25 6:48 ` Arnd Bergmann
2020-06-25 14:38 ` André Almeida
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAMe9rOqnBRzXv4xnhFvOgdVpDo0oRc1SYq38zcJWo9BPZseagg@mail.gmail.com \
--to=hjl.tools@gmail.com \
--cc=andrealmeid@collabora.com \
--cc=dvhart@infradead.org \
--cc=fweimer@redhat.com \
--cc=kernel@collabora.com \
--cc=krisman@collabora.com \
--cc=libc-alpha@sourceware.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=malteskarupke@web.de \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=pgriffais@valvesoftware.com \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).