linux-kernel - Re: [patch 00/11] ANNOUNCE: "Syslets", generic asynchronous system call support

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Date:	Wed, 14 Feb 2007 13:36:13 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	Evgeniy Polyakov <johnpol@....mipt.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 00/11] ANNOUNCE: "Syslets", generic asynchronous system
 call support

On Wed, 14 Feb 2007, Jeremy Fitzhardinge wrote:

> Are there any special semantics that result from running the syslet
> atoms in kernel mode?  If I wanted to, could I write a syslet emulation
> in userspace that's functionally identical to a kernel-based
> implementation?  (Obviously the performance characteristics will be
> different.)
> 
> I'm asking from the perspective of trying to work out the Valgrind
> binding for this if it goes into the kernel.  Valgrind needs to see all
> the input and output values of each system call the client makes,
> including those done within the syslet mechanism.  It seems to me that
> the easiest way to do this would be to intercept the syslet system
> calls, and just implement them in usermode, performing the same series
> of syscalls directly, and applying the Valgrind machinery to each one in
> turn.
> 
> Would this work?

Hopefully the API will simplify enough so that emulation will becomes 
easier.



> Also, an unrelated question: is there enough control structure in place
> to allow multiple syslet streams to synchronize with each other with
> futexes?

I think the whole point of an async execution of a syscall or a syslet, is 
that the syscall/syslet itself includes a non interlocked operations with 
other syscalls/syslets. So that the main scheduler thread can run in a 
lockless/singletask fashion. There are no technical obstacles that 
prevents you to do it, bu if you start adding locks (and hence having 
long-living syslet-threads) at that point you'll end up with a fully 
multithreaded solution.



- Davide


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