From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946076AbXBBVG0 (ORCPT ); Fri, 2 Feb 2007 16:06:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1946077AbXBBVG0 (ORCPT ); Fri, 2 Feb 2007 16:06:26 -0500 Received: from x35.xmailserver.org ([64.71.152.41]:2765 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1946076AbXBBVGZ (ORCPT ); Fri, 2 Feb 2007 16:06:25 -0500 X-Greylist: delayed 488 seconds by postgrey-1.27 at vger.kernel.org; Fri, 02 Feb 2007 16:06:25 EST X-AuthUser: davidel@xmailserver.org Date: Fri, 2 Feb 2007 12:58:09 -0800 (PST) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Linus Torvalds cc: Alan , Ingo Molnar , Zach Brown , Linux Kernel Mailing List , linux-aio@kvack.org, Suparna Bhattacharya , Benjamin LaHaise Subject: Re: [PATCH 2 of 4] Introduce i386 fibril scheduling In-Reply-To: Message-ID: References: <20070201083611.GC18233@elte.hu> <20070202104900.GA13941@elte.hu> <20070202195932.15b9b4ed@localhost.localdomain> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="1795850513-519671827-1170449889=:5219" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. --1795850513-519671827-1170449889=:5219 Content-Type: TEXT/PLAIN; charset=US-ASCII On Fri, 2 Feb 2007, Linus Torvalds wrote: > > You get some other funny things from co-routines which are very powerful, > > very dangerous, or plain insane > > You forgot "very hard to think about". > > We DO NOT want coroutines in general. It's clever, but it's > (a) impossible to do without language support that C doesn't have, or > some really really horrid macro constructs that really only work for > very specific and simple cases. > (b) very non-intuitive unless you've worked with coroutines a lot (and > almost nobody has) Actually, coroutines are not too bad to program once you have a total-coverage async scheduler to run them. The attached (very sketchy) example uses libpcl ( http://www.xmailserver.org/libpcl.html ) and epoll as scheduler (but here you can really use anything). You can implement coroutines in many way, from C preprocessor macros up to anything, but in the libpcl case they are simply switched stacks. Like fibrils are supposed to be. The problem is that in order to make a real-life example of coroutine-based application work, you need everything that can put you at sleep (syscalls or any external library call you have no control on) implemented in an async way. And what I ended up doing is exactly what Zab did inside the kernel. In my case a dynamic pool of (userspace) threads servicing any non-native potentially pre-emptive call, and signaling the result to a pollable fd (pipe in my case) that is integrated in the epoll (poll/select whatever) scheduler. I personally find Zab idea a really good one, since it allows for generic kernel async implementation, w/out the burden of dirtying kernel code paths with AIO knowledge. Being it fibrils or real kthreads, it is IMO definitely worth a very close look. - Davide --1795850513-519671827-1170449889=:5219 Content-Type: TEXT/x-csrc; charset=US-ASCII; name=cotest.c Content-Transfer-Encoding: BASE64 Content-Description: Content-Disposition: attachment; filename=cotest.c DQpzdHJ1Y3QgZXBoX2Nvbm4gew0KCWludCBzZmQ7DQoJdW5zaWduZWQgaW50 IGV2ZW50cywgcmV2ZW50czsNCgljb3JvdXRpbmVfdCBjbzsNCn07DQoNCg0K DQppbnQgZXBoX25ld19jb25uKGludCBzZmQsIHZvaWQgKmZ1bmMpIHsNCglz dHJ1Y3QgZXBoX2Nvbm4gKmNvbm47DQoJc3RydWN0IGVwb2xsX2V2ZW50IGV2 Ow0KDQoJY29ubiA9IChzdHJ1Y3QgZXBoX2Nvbm4gKikgbWFsbG9jKHNpemVv ZihzdHJ1Y3QgZXBoX2Nvbm4pKTsNCg0KCWNvbm4tPnNmZCA9IHNmZDsNCglj b25uLT5jbyA9IGNvX2NyZWF0ZShmdW5jLCBjb25uLCBOVUxMLCBTVEFDS1NJ WkUpOw0KDQoJZXYuZXZlbnRzID0gMDsNCglldi5kYXRhLnB0ciA9IGNvbm47 DQoJZXBvbGxfY3RsKGtkcGZkLCBFUE9MTF9DVExfQURELCBzZmQsICZldik7 DQoNCgljb19jYWxsKGNvbm4tPmNvKTsNCg0KCXJldHVybiAwOw0KfQ0KDQp2 b2lkIGVwaF9leGl0X2Nvbm4oc3RydWN0IGVwaF9jb25uICpjb25uKSB7DQoJ c3RydWN0IGVwb2xsX2V2ZW50IGV2Ow0KDQoJZXBvbGxfY3RsKGtkcGZkLCBF UE9MTF9DVExfREVMLCBjb25uLT5zZmQsICZldik7DQoJY29fZXhpdCgpOw0K fQ0KDQppbnQgZXBoX2Nvbm5lY3Qoc3RydWN0IGVwaF9jb25uICpjb25uLCBj b25zdCBzdHJ1Y3Qgc29ja2FkZHIgKnNlcnZfYWRkciwgc29ja2xlbl90IGFk ZHJsZW4pIHsNCg0KCWlmIChjb25uZWN0KGNvbm4tPnNmZCwgc2Vydl9hZGRy LCBhZGRybGVuKSA9PSAtMSkgew0KCQlpZiAoZXJybm8gIT0gRVdPVUxEQkxP Q0sgJiYgZXJybm8gIT0gRUlOUFJPR1JFU1MpDQoJCQlyZXR1cm4gLTE7DQoJ CWNvX3Jlc3VtZSgpOw0KCQlpZiAoY29ubi0+cmV2ZW50cyAmIChFUE9MTEVS UiB8IEVQT0xMSFVQKSkNCgkJCXJldHVybiAtMTsNCgl9DQoJcmV0dXJuIDA7 DQp9DQoNCmludCBlcGhfcmVhZChzdHJ1Y3QgZXBoX2Nvbm4gKmNvbm4sIHZv aWQgKmJ1ZiwgaW50IG5ieXRlKSB7DQoJaW50IG47DQoNCgl3aGlsZSAoKG4g PSByZWFkKGNvbm4tPnNmZCwgYnVmLCBuYnl0ZSkpIDwgMCkgew0KCQlpZiAo ZXJybm8gPT0gRUlOVFIpDQoJCQljb250aW51ZTsNCgkJaWYgKGVycm5vICE9 IEVBR0FJTiAmJiBlcnJubyAhPSBFV09VTERCTE9DSykNCgkJCXJldHVybiAt MTsNCgkJY29fcmVzdW1lKCk7DQoJfQ0KCXJldHVybiBuOw0KfQ0KDQppbnQg ZXBoX3dyaXRlKHN0cnVjdCBlcGhfY29ubiAqY29ubiwgdm9pZCBjb25zdCAq YnVmLCBpbnQgbmJ5dGUpIHsNCglpbnQgbjsNCg0KCXdoaWxlICgobiA9IHdy aXRlKGNvbm4tPnNmZCwgYnVmLCBuYnl0ZSkpIDwgMCkgew0KCQlpZiAoZXJy bm8gPT0gRUlOVFIpDQoJCQljb250aW51ZTsNCgkJaWYgKGVycm5vICE9IEVB R0FJTiAmJiBlcnJubyAhPSBFV09VTERCTE9DSykNCgkJCXJldHVybiAtMTsN CgkJY29fcmVzdW1lKCk7DQoJfQ0KCXJldHVybiBuOw0KfQ0KDQppbnQgZXBo X2FjY2VwdChzdHJ1Y3QgZXBoX2Nvbm4gKmNvbm4sIHN0cnVjdCBzb2NrYWRk ciAqYWRkciwgaW50ICphZGRybGVuKSB7DQoJaW50IHNmZDsNCg0KCXdoaWxl ICgoc2ZkID0gYWNjZXB0KGNvbm4tPnNmZCwgYWRkciwgKHNvY2tsZW5fdCAq KSBhZGRybGVuKSkgPCAwKSB7DQoJCWlmIChlcnJubyA9PSBFSU5UUikNCgkJ CWNvbnRpbnVlOw0KCQlpZiAoZXJybm8gIT0gRUFHQUlOICYmIGVycm5vICE9 IEVXT1VMREJMT0NLKQ0KCQkJcmV0dXJuIC0xOw0KCQljb19yZXN1bWUoKTsN Cgl9DQoJcmV0dXJuIHNmZDsNCn0NCg0KaW50IGVwaF9zY2hlZHVsZXIoaW50 IGxvb3AsIGxvbmcgdGltZW91dCkgew0KCWludCBpLCBuZmRzOw0KCXN0cnVj dCBlcGhfY29ubiAqY29ubjsNCglzdHJ1Y3QgZXBvbGxfZXZlbnQgKmNldmVu dHM7DQoNCglkbyB7DQoJCW5mZHMgPSBlcG9sbF93YWl0KGtkcGZkLCBldmVu dHMsIG1heGZkcywgdGltZW91dCk7DQoNCgkJZm9yIChpID0gMCwgY2V2ZW50 cyA9IGV2ZW50czsgaSA8IG5mZHM7IGkrKywgY2V2ZW50cysrKSB7DQoJCQlj b25uID0gY2V2ZW50cy0+ZGF0YS5wdHI7DQoJCQljb25uLT5yZXZlbnRzID0g Y2V2ZW50cy0+ZXZlbnRzOw0KCQkJaWYgKGNvbm4tPnJldmVudHMgJiBjb25u LT5ldmVudHMpDQoJCQkJY29fY2FsbChjb25uLT5jbyk7DQoJCX0NCgl9IHdo aWxlIChsb29wKTsNCg0KCXJldHVybiAwOw0KfQ0KDQo= --1795850513-519671827-1170449889=:5219--