linux-kernel - Re: [PATCH 2 of 4] Introduce i386 fibril scheduling

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Date:	Tue, 6 Feb 2007 12:25:00 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Kent Overstreet <kent.overstreet@...il.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Zach Brown <zach.brown@...cle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-aio@...ck.org, Suparna Bhattacharya <suparna@...ibm.com>,
	Benjamin LaHaise <bcrl@...ck.org>
Subject: Re: [PATCH 2 of 4] Introduce i386 fibril scheduling

On Mon, 5 Feb 2007, Kent Overstreet wrote:

> > > HOWEVER, they get returned differently. The cookie gets returned
> > > immediately, the system call result gets returned in-memory only after the
> > > async thing has actually completed.
> > >
> > > I would actually argue that it's not the kernel that should generate any
> > > cookie, but that user-space should *pass*in* the cookie it wants to, and
> > > the kernel should consider it a pointer to a 64-bit entity which is the
> > > return code.
> > 
> > Yes. Let's have the userspace to "mark" the async operation. IMO the
> > cookie should be something transparent to the kernel.
> > Like you said though, that'd require compat-code (unless we fix the size).
> 
> You don't need an explicit cookie if you're passing in a pointer to
> the return code, it doesn't really save you anything to do so. Say
> you've got a bunch of user threads (with or without stacks, it doesn't
> matter).
> 
> struct asys_ret {
>     int ret;
>     struct thread *p;
> };
> 
> struct asys_ret r;
> r.p = me;
> 
> async_read(fd, buf, nbytes, &r);

Hmm, are you working for Symbian? Because that's exactly how they track 
pending async operations (address of a status variable - wrapped in a 
class of course, being them) ;)
That's another way of doing it, IMO no better no worse than letting 
explicit cookie selection from userspace. You still have to have the 
compat code though, either ways.



- Davide


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