Linux-kselftest Archive on lore.kernel.org
 help / color / Atom feed
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
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?

  reply index

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

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=20200228194958.GO14946@hirez.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=andrealmeid@collabora.com \
    --cc=dvhart@infradead.org \
    --cc=kernel@collabora.com \
    --cc=krisman@collabora.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=malteskarupke@web.de \
    --cc=mingo@redhat.com \
    --cc=pgriffais@valvesoftware.com \
    --cc=rostedt@goodmis.org \
    --cc=ryao@gentoo.org \
    --cc=shuah@kernel.org \
    --cc=steven@liquorix.net \
    --cc=steven@valvesoftware.com \
    --cc=tglx@linutronix.de \
    --cc=z.figura12@gmail.com \
    /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

Linux-kselftest Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-kselftest/0 linux-kselftest/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-kselftest linux-kselftest/ https://lore.kernel.org/linux-kselftest \
		linux-kselftest@vger.kernel.org
	public-inbox-index linux-kselftest

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kselftest


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git