linux-kernel - Re: [patch 05/11] syslets: core code

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Date:	Thu, 15 Feb 2007 13:17:14 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Evgeniy Polyakov <johnpol@....mipt.ru>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.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>,
	"David S. Miller" <davem@...emloft.net>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 05/11] syslets: core code

On Thu, 15 Feb 2007, Linus Torvalds wrote:

> 
> 
> On Thu, 15 Feb 2007, Linus Torvalds wrote:
> > 
> > So I think that a good implementation just does everything up-front, and 
> > doesn't _need_ a user buffer that is live over longer periods, except for 
> > the actual results. Exactly because the whole alloc/teardown is nasty.
> 
> Btw, this doesn't necessarily mean "not supporting multiple atoms at all".
> 
> I think the batching of async things is potentially a great idea. I think 
> it's quite workable for "open+fstat" kind of things, and I agree that it 
> can solve other things too (the "socket+bind+connect+sendmsg+rcv" kind of 
> complex setup things).

If you *really* want to allow chains (note that the above could be 
prolly be hosted on a real thread, once chains becomes that long), then 
try to build that chain with the current API, and compare it with:

long my_clet(ctx *c) {
	int fd, error = -1;

	if ((fd = socket(...)) == -1 ||
	    bind(fd, &c->laddr, sizeof(c->laddr)) ||
	    connect(fd, &c->saddr, sizeof(c->saddr)) ||
	    sendmsg(fd, ...) == -1 ||
	    recv(fd, ...) <= 0)
		goto
	error = 0;
erxit:
	close(fd);
	return error;
}

Points:

- Keep the submission API to submit one or an array of parallel async 
  syscalls/clets

- Keep arguments of the syscall being longs (no need for extra pointer 
  indirection compat code, and special copy_atoms functions)

- No need for the "next" atom pointer chaining (nice for compat too)

- No need to create special conditions/jump interpreters into the kernel 
  (nice for compat and emulators). C->machine-code that that for us

- Easier to code. Try to build a chain like that with the current API and 
  you will see what I saying

- Did I say faster? Machine code is faster than sudo-VM interpretation of 
  jumps/conditions done inside the kernel




- Davide


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