linux-kernel - Re: poll: allow f_op->poll to sleep, take #3

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Date:	Sun, 23 Nov 2008 20:57:39 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Tejun Heo <htejun@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <matthew@....cx>,
	Miklos Szeredi <miklos@...redi.hu>, arjan@...ux.intel.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	hch@...radead.org, rminnich@...dia.gov, ericvh@...il.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: poll: allow f_op->poll to sleep, take #3

On Mon, 24 Nov 2008, Tejun Heo wrote:

> Ingo Molnar wrote:
> >> And @sync might be useful depending on who's waking it up, so we 
> >> either need to change the wake interface or give it an easier way to 
> >> pass those parameters as received.  The callback function isn't the 
> >> right place to ignore those parameters.  It simply doesn't know why 
> >> the caller is passing them in or what they mean under the 
> >> circumstances.
> > 
> > We'll likely eliminate the 'sync' parameter from the scheduler. It's 
> > not a flag that should be proliferated.
> 
> But it's still being used in quite hot paths (pipe, splice, socket)
> and I don't really wanna mix up a change which can cause subtle
> scheduling related performance regression into this patch.  How about
> using the dummy waitqueue hack for now and when removing the @sync
> param, switch it to one of wakeup APIs?  I'll be happy to add big /*
> TODO */ comment in the function.

I was noticing that wake ups on the poll queues do not use sync=1, AFAICS.
So using wake_up_state() and ignoring 'sync' should be fine. And 'key' is 
already ignored by default by default_wake_function().



- Davide


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