linux-kernel - Re: [patch 1/2] epoll fix own poll()

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Date:	Fri, 30 Jan 2009 10:40:51 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Pavel Pisa <pisa@....felk.cvut.cz>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch 1/2] epoll fix own poll()

On Fri, 30 Jan 2009, Pavel Pisa wrote:

> I have seen the reason exactly when I have sent the e-mail
> and switched computer off at the night.
> 
> The reason is simple and it is caused by debugging print in each
> loop in my application and by way how poll concept is implemented
> in the kernel.

Yes, this is a known thing. Like I already told you yesterday, calling it 
a "spurious" event. So you code *is* generating a spurios event to the 
tty, with a write.
Unfortunately this is how Linux poll subsystem works. But things can be 
improved, w/out any revolution.
I already have patches to send Andrew-ward, that (gradually) uses the 
wakeup "key" to report event that really happened, during the wakeup call. 
This will allow the epoll callback to avoid epoll waiters wakeups, when 
events do not match the interest mask.

- Davide

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