linux-kernel - Re: [patch 3/7] epoll keyed wakeups - introduce key-aware wakeup macros

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Date:	Sat, 31 Jan 2009 16:28:32 -0500
From:	wli@...ementarian.org
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...e.hu>, David Miller <davem@...emloft.net>
Subject: Re: [patch 3/7] epoll keyed wakeups - introduce key-aware wakeup macros

On Fri, 30 Jan 2009, wli@...ementarian.org wrote:
>> The filtered wakeup code uses some notion of a key already. There, the
>> key is to route wakeups to recipients associated with the correct
>> object. Here, the objects are known in advance. The wakeup is to give
>> them some particular message in which they may not necessarily be
>> interested. Names indicative of that (e.g. *_msg/msg_*) would clarify
>> the distinction between it and the filtered wakeup code used for pages.

On Sat, Jan 31, 2009 at 11:08:40AM -0800, Davide Libenzi wrote:
> I had thought of giving the void* some structure, besides being a cast 
> from an event mask, so that later on we'd be able to eventually embed 
> more information in the wakeup. Dunno if worth it.

kernel/wait.c uses struct wait_bit_key; void * was merely for keeping it
as private as possible, though it is exposed for the sake of macros like
DEFINE_WAIT_BIT et al. It would make little difference to the pagecache
waitqueue code if the structure were augmented, the function prototypes
changed to reflect the argument type, etc. There are a priori guarantees
based on the objects that the lists of tasks considered won't overlap,
so unrelated structures are even possible.


-- wli
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