linux-kernel - Re: [PATCH RFC 2/2] futex: Implement mechanism to wait on any of several futexes

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Date:   Thu, 1 Aug 2019 00:39:10 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Zebediah Figura <z.figura12@...il.com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        mingo@...hat.com, dvhart@...radead.org,
        linux-kernel@...r.kernel.org, kernel@...labora.com,
        Steven Noonan <steven@...vesoftware.com>,
        "Pierre-Loup A . Griffais" <pgriffais@...vesoftware.com>,
        viro@...iv.linux.org.uk, jannh@...gle.com
Subject: Re: [PATCH RFC 2/2] futex: Implement mechanism to wait on any of
 several futexes

On Wed, 31 Jul 2019, Zebediah Figura wrote:
> On 7/31/19 7:06 AM, Peter Zijlstra wrote:
> > On Tue, Jul 30, 2019 at 06:06:02PM -0400, Gabriel Krisman Bertazi wrote:
> > > This is a new futex operation, called FUTEX_WAIT_MULTIPLE, which allows
> > > a thread to wait on several futexes at the same time, and be awoken by
> > > any of them.  In a sense, it implements one of the features that was
> > > supported by pooling on the old FUTEX_FD interface.
> > > 
> > > My use case for this operation lies in Wine, where we want to implement
> > > a similar interface available in Windows, used mainly for event
> > > handling.  The wine folks have an implementation that uses eventfd, but
> > > it suffers from FD exhaustion (I was told they have application that go
> > > to the order of multi-milion FDs), and higher CPU utilization.
> > 
> > So is multi-million the range we expect for @count ?
> > 
> 
> Not in Wine's case; in fact Wine has a hard limit of 64 synchronization
> primitives that can be waited on at once (which, with the current user-side
> code, translates into 65 futexes). The exhaustion just had to do with the
> number of primitives created; some programs seem to leak them badly.

And how is the futex approach better suited to 'fix' resource leaks?

Thanks,

	tglx