From: Peter Zijlstra <peterz@infradead.org>
To: "André Almeida" <andrealmeid@collabora.com>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
kernel@collabora.com, krisman@collabora.com, shuah@kernel.org,
linux-kselftest@vger.kernel.org, rostedt@goodmis.org,
ryao@gentoo.org, dvhart@infradead.org, mingo@redhat.com,
z.figura12@gmail.com, steven@valvesoftware.com,
pgriffais@valvesoftware.com, steven@liquorix.net,
malteskarupke@web.de
Subject: Re: [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes
Date: Fri, 28 Feb 2020 20:49:58 +0100 [thread overview]
Message-ID: <20200228194958.GO14946@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200228190717.GM18400@hirez.programming.kicks-ass.net>
On Fri, Feb 28, 2020 at 08:07:17PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 13, 2020 at 06:45:22PM -0300, André Almeida wrote:
> > @@ -150,4 +153,21 @@ struct robust_list_head {
> > (((op & 0xf) << 28) | ((cmp & 0xf) << 24) \
> > | ((oparg & 0xfff) << 12) | (cmparg & 0xfff))
> >
> > +/*
> > + * Maximum number of multiple futexes to wait for
> > + */
> > +#define FUTEX_MULTIPLE_MAX_COUNT 128
> > +
> > +/**
> > + * struct futex_wait_block - Block of futexes to be waited for
> > + * @uaddr: User address of the futex
> > + * @val: Futex value expected by userspace
> > + * @bitset: Bitset for the optional bitmasked wakeup
> > + */
> > +struct futex_wait_block {
> > + __u32 __user *uaddr;
> > + __u32 val;
> > + __u32 bitset;
> > +};
>
> So I have a problem with this vector layout, it doesn't allow for
> per-futex flags, and esp. with that multi-size futex support that
> becomes important, but also with the already extand private/shared and
> wait_bitset flags this means you cannot have a vector with mixed wait
> types.
Alternatively, we throw the entire single-syscall futex interface under
the bus and design a bunch of new syscalls that are natively vectored or
something.
Thomas mentioned something like that, the problem is, ofcourse, that we
then want to fix a whole bunch of historical ills, and the probmem
becomes much bigger.
Thomas?
next prev parent reply other threads:[~2020-02-28 19:50 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-13 21:45 [PATCH v3 0/4] Implement FUTEX_WAIT_MULTIPLE operation André Almeida
2020-02-13 21:45 ` [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes André Almeida
2020-02-28 19:07 ` Peter Zijlstra
2020-02-28 19:49 ` Peter Zijlstra [this message]
2020-02-28 21:25 ` Thomas Gleixner
2020-02-29 0:29 ` Pierre-Loup A. Griffais
2020-02-29 10:27 ` Thomas Gleixner
2020-03-03 2:47 ` Pierre-Loup A. Griffais
2020-03-03 12:00 ` 'simple' futex interface [Was: [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes] Peter Zijlstra
2020-03-03 13:00 ` Florian Weimer
2020-03-03 13:21 ` Peter Zijlstra
2020-03-03 13:47 ` Florian Weimer
2020-03-03 15:01 ` Peter Zijlstra
2020-03-05 16:14 ` André Almeida
2020-03-05 16:25 ` Florian Weimer
2020-03-05 18:51 ` Peter Zijlstra
2020-03-06 16:57 ` David Laight
2020-02-13 21:45 ` [PATCH v3 2/4] selftests: futex: Add FUTEX_WAIT_MULTIPLE timeout test André Almeida
2020-02-13 21:45 ` [PATCH v3 3/4] selftests: futex: Add FUTEX_WAIT_MULTIPLE wouldblock test André Almeida
2020-02-13 21:45 ` [PATCH v3 4/4] selftests: futex: Add FUTEX_WAIT_MULTIPLE wake up test André Almeida
2020-02-19 16:27 ` [PATCH v3 0/4] Implement FUTEX_WAIT_MULTIPLE operation shuah
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