linux-kernel - Re: [ltt-dev] [RFC PATCH] Poll : add poll_wait_set_exclusive (fixing thundering herd problem in LTTng)

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Message-Id: <20081124205512.26C1.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Mon, 24 Nov 2008 21:11:28 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	kosaki.motohiro@...fujitsu.com, ltt-dev@...ts.casi.polymtl.ca,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	William Lee Irwin III <wli@...omorphy.com>
Subject: Re: [ltt-dev] [RFC PATCH] Poll : add poll_wait_set_exclusive (fixing thundering herd problem in LTTng)

> > I fully agreed this feature is needed.
> > Actually, I've made similar patch at one years ago.
> > 
> > http://marc.info/?l=linux-kernel&m=120257050719087&w=2
> > 
> > 
> > but, I have one question.
> > My version have epoll support, but yours donesn't have.
> > Is it intensionally?
> > 
> > this is just dumb question, it doesn't mean any objection.
> 
> Hrm, actually, your patch seems cleaner than mine, but it adds a branch
> in the standard hotpath, which mine does not do (but I am not sure it is
> such an important optimization...). 

Why do you think poll_wait() is hotpath?
I think sysm_poll() isn't hotpath because it often cause task sleeping.


> Is there any reason why your patch
> did not get merged ?

my patch was developed for a part of mem_notify patch series.
but the mem_notify was naked by akpm.
therefore it lost merging motivation ;-)

Ingo, I'll rebase and post my patch for -tip tommorow.
Could you please review it?


> The only reason I did not make a epoll version is simply because LTTng
> currently does not support it. :)

thanks.
I understand your original intension.



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