linux-kernel - Re: [take12 0/3] kevent: Generic event handling mechanism.

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Message-Id: <20060823090920.18e4d1da.akpm@osdl.org>
Date:	Wed, 23 Aug 2006 09:09:20 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	Jari Sundell <sundell.software@...il.com>,
	David Miller <davem@...emloft.net>, kuznet@....inr.ac.ru,
	nmiell@...cast.net, linux-kernel@...r.kernel.org,
	drepper@...hat.com, netdev@...r.kernel.org, zach.brown@...cle.com,
	hch@...radead.org
Subject: Re: [take12 0/3] kevent: Generic event handling mechanism.

On Wed, 23 Aug 2006 11:50:56 +0400
Evgeniy Polyakov <johnpol@....mipt.ru> wrote:

> On Wed, Aug 23, 2006 at 12:07:58AM -0700, Andrew Morton (akpm@...l.org) wrote:
> > On Wed, 23 Aug 2006 10:56:59 +0400
> > Evgeniy Polyakov <johnpol@....mipt.ru> wrote:
> > 
> > > On Wed, Aug 23, 2006 at 02:43:50AM +0200, Jari Sundell (sundell.software@...il.com) wrote:
> > > > Actually, I didn't miss that, it is an orthogonal issue. A timespec
> > > > timeout parameter for the syscall does not imply the use of timespec
> > > > in any timer event, etc. Nor is there any timespec timer in kqueue's
> > > > struct kevent, which is the only (interface related) thing that will
> > > > be exposed.
> > > 
> > > void * in structure exported to userspace is forbidden.
> > > long in syscall requires wrapper in per-arch code (although that
> > > workaround _is_ there, it does not mean that broken interface should 
> > > be used).
> > > poll uses millisecods - it is perfectly ok.
> > 
> > I wonder whether designing-in a millisecond granularity is the right thing
> > to do.  If in a few years the kernel is running tickless with high-res clock
> > interrupt sources, that might look a bit lumpy.
> > 
> > Switching it to a __u64 nanosecond counter would be basically free on
> > 64-bit machines, and not very expensive on 32-bit, no?
> 
> I can put nanoseconds as timer interval too (with aligned_u64 as David
> mentioned), and put it for timeout value too - 64 bit nanosecods ends up
> with 58 years, probably enough.
> Structures with u64 a really not so good idea.
> 

OK.  One could do u32 seconds/u32 nsecs, but a simple aligned_u64 will be
better for 64-bit machines, and OK for 32-bit.
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