Return-path: Received: from mail-iw0-f175.google.com ([209.85.223.175]:44499 "EHLO mail-iw0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751631AbZIHEQ6 convert rfc822-to-8bit (ORCPT ); Tue, 8 Sep 2009 00:16:58 -0400 MIME-Version: 1.0 In-Reply-To: <1252376254.21261.2052.camel@gandalf.stny.rr.com> References: <43e72e890909071558s637b45c7i10807587dc40e8c4@mail.gmail.com> <20090907171406.6a4b6116@nehalam> <1252376254.21261.2052.camel@gandalf.stny.rr.com> From: "Luis R. Rodriguez" Date: Mon, 7 Sep 2009 21:16:38 -0700 Message-ID: <43e72e890909072116v33ecafc4ma7f5a68825f14e9@mail.gmail.com> Subject: Re: Stop using tasklets for bottom halves To: rostedt@goodmis.org Cc: Stephen Hemminger , Ingo Molnar , Michael Buesch , "John W. Linville" , linux-wireless , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Matt Smith , Kevin Hayes , Bob Copeland , Jouni Malinen , Ivan Seskar , ic.felix@gmail.com Content-Type: text/plain; charset=UTF-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Mon, Sep 7, 2009 at 7:17 PM, Steven Rostedt wrote: > On Mon, 2009-09-07 at 17:14 -0700, Stephen Hemminger wrote: >> On Mon, 7 Sep 2009 15:58:50 -0700 >> "Luis R. Rodriguez" wrote: >> >> > A while ago I had read about an effort to consider removing tasklets >> > [1] or at least trying to not use them. I'm unaware of the progress in >> > this respect but since reading that article have always tried to >> > evaluate whether or not we need tasklets on wireless drivers. I have >> > also wondered whether work in irq context in other parts of the kernel >> > can be moved to process context, a curious example being timers. I'll >> > personally be trying to using only process context on bottom halves on >> > future drivers but I figured it may be a good time to ask how serious >> > was avoiding tasklets or using wrappers in the future to avoid irq >> > context is or is it advised. Do we have a general agreement this is a >> > good step forward to take? Has anyone made tests or changes on a >> > specific driver from irq context to process context and proven there >> > are no significant advantages of using irq context where you would >> > have expected it? >> > >> > Wireless in particular should IMHO not require taskets for anything >> > time sensitive that I can think about except perhaps changing channels >> > quickly and to do that appropriately also process pending RX frames >> > prior to a switch. It remains to be seen experimentally whether or not >> > using a workqueue for RX processing would affect the time to switch >> > channels negatively but I doubt it would be significant. I hope to >> > test that with ath9k_htc. >> > >> > What about gigabit or 10 Gigabit Ethernet drivers ? Do they face any >> > challenges which would yet need to be proven would not face issues >> > when processing bottom halves in process context? >> > >> > [1] http://lwn.net/Articles/239633/ >> > >> >   Luis >> > -- >> > To unsubscribe from this list: send the line "unsubscribe netdev" in >> > the body of a message to majordomo@vger.kernel.org >> > More majordomo info at  http://vger.kernel.org/majordomo-info.html >> >> Why not use NAPI, which is soft irq? Almost all 1G and 10G drivers >> use NAPI. >> >> Process context is too slow. > > Well, I'm hoping to prove the opposite. I'm working on some stuff that I > plan to present at Linux Plumbers. I've been too distracted by other > things, but hopefully I'll have some good numbers to present by then. What day in specific was this planned for at Plumbers? Luis