linux-kernel - Re: [patch 14/22] pollfs: pollable futex

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Date:	Wed, 2 May 2007 10:49:36 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	"Ulrich Drepper" <drepper@...il.com>
Cc:	"Davi Arnaut" <davi@...ent.com.br>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Davide Libenzi" <davidel@...ilserver.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [patch 14/22] pollfs: pollable futex

On Wed, 2 May 2007 01:08:26 -0700
"Ulrich Drepper" <drepper@...il.com> wrote:

> On 5/2/07, Eric Dumazet <dada1@...mosbay.com> wrote:
> > Well, poll() level edge semantic is well defined, you cannot cheat or change it.
> >
> > If many threads call poll() on the same end point, they should *all* return POLLIN/whatever status.
> 
> This means to me it's the wrong abstraction for this.  We had a nice
> solution for this with Evgeniy's kevent interfaces.  It worked without
> forcing futexes is this inflexible poll() interface.

poll() is a generalist interface. Not the *perfect* one, but well spreaded on other OS as well.

> 
> 
> 
> > This is why programs usually use one thread to dispatch events to workers, or at least dont queue XXXX threads calling poll() on one fd.
> 
> No.  This is why programs are forced to waste cycles by doing this.
> Ideally this would not happen.  Ideally you'd park all worker thread
> in the same place and have them woken up one by one.  Again, Evgeniy's
> code was able to do this.  This approach seems to be a big step
> backward.

I understand your concerns, but *this* patch bundle extends poll()/select()/epoll, and is not an alternative to kevent or other work in progress, (and linux centered)

Are you suggesting poll() system call should be deprecated ?

Most programs still use the archaic select() thing you know ...

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