From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753335AbXCaTrI (ORCPT ); Sat, 31 Mar 2007 15:47:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753362AbXCaTrI (ORCPT ); Sat, 31 Mar 2007 15:47:08 -0400 Received: from x35.xmailserver.org ([64.71.152.41]:48153 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753335AbXCaTrG (ORCPT ); Sat, 31 Mar 2007 15:47:06 -0400 X-AuthUser: davidel@xmailserver.org Date: Sat, 31 Mar 2007 12:46:58 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Andrew Morton cc: Linux Kernel Mailing List , Linus Torvalds , Thomas Gleixner Subject: Re: [patch 6/13] signal/timer/event fds v8 - timerfd core ... In-Reply-To: <20070330180910.dd16a52f.akpm@linux-foundation.org> Message-ID: References: <20070330124005.0ec31aa6.akpm@linux-foundation.org> <20070330180910.dd16a52f.akpm@linux-foundation.org> 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: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 30 Mar 2007, Andrew Morton wrote: > On Fri, 30 Mar 2007 17:47:28 -0700 (PDT) Davide Libenzi wrote: > > > On Fri, 30 Mar 2007, Andrew Morton wrote: > > > > > > +struct timerfd_ctx { > > > > + struct hrtimer tmr; > > > > + ktime_t tintv; > > > > + spinlock_t lock; > > > > + wait_queue_head_t wqh; > > > > + unsigned long ticks; > > > > +}; > > > > > > Did you consider using the (presently unused) lock inside wqh instead of > > > adding a new one? That's a little bit rude, poking into waitqueue > > > internals like that, but we do it elsewhere and tricks like that are > > > acceptable in core-kernel, I guess. > > > > Please, no. Gain is not worth the plug into the structure design IMO. > > > > The decision is not that obvious - your patch's main use of > timerfd_ctx.lock is to provide locking for wqh - ie: to duplicate the > function of the existing lock which is there for that purpose. > > So I think it's a legitimate optimisation to borrow it. As I see it, the lock protects the ticks and the timer structure, and the wait queue *happen* to have a lock inside. That's the whole purpose in having data modeled by structures with accessor functions. IMO, given that we'd get by plugging into the wait_queue_head_t lock is not much (if at all), it'd be better to to peek at the wait_queue_head_t directly. > > > > +static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr) > > > > +{ > > > > + struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr); > > > > + enum hrtimer_restart rval = HRTIMER_NORESTART; > > > > + unsigned long flags; > > > > + > > > > + spin_lock_irqsave(&ctx->lock, flags); > > > > + ctx->ticks++; > > > > + wake_up_locked(&ctx->wqh); > > > > + if (ctx->tintv.tv64 != 0) { > > > > + hrtimer_forward(htmr, hrtimer_cb_get_time(htmr), ctx->tintv); > > > > + rval = HRTIMER_RESTART; > > > > + } > > > > + spin_unlock_irqrestore(&ctx->lock, flags); > > > > + > > > > + return rval; > > > > +} > > > > > > What's this do? > > > > Really, do we need to comment such trivial code? There is *nothing* that > > is worth a line of comment in there. IMO useless comment are more annoying > > than blank lines. > > > > Look at it from the point of view of someone who knows kernel code but does > not specifically know this subsystem. That describes the great majority of > people who will be reading your code. Okie, I added a comment ;) > Patch headers are not maintainable. > > Nobody wants to have to go off and waddle though the git repo to understand > the design intent behind each function. I agree. I thought we were talking about the "poor smuck" having to document it, and the patch header is a pretty good start (and maybe finish ;). - Davide