Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752543AbbETBoT (ORCPT ); Tue, 19 May 2015 21:44:19 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:51282 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750822AbbETBoQ (ORCPT ); Tue, 19 May 2015 21:44:16 -0400 Date: Tue, 19 May 2015 18:44:08 -0700 From: Guenter Roeck To: Joe Perches Cc: David Miller , hofrat@osadl.org, samuel@sortiz.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] irda: irda-usb: use msecs_to_jiffies for conversions Message-ID: <20150520014408.GA19321@roeck-us.net> References: <1432032711-7020-1-git-send-email-hofrat@osadl.org> <1432045935.2870.152.camel@perches.com> <20150519.164555.1631069770118420652.davem@davemloft.net> <1432069747.2870.215.camel@perches.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1432069747.2870.215.camel@perches.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Authenticated_sender: guenter@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: guenter@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1877 Lines: 42 On Tue, May 19, 2015 at 02:09:07PM -0700, Joe Perches wrote: > On Tue, 2015-05-19 at 16:45 -0400, David Miller wrote: > > From: Joe Perches > > Date: Tue, 19 May 2015 07:32:15 -0700 > > > > > On Tue, 2015-05-19 at 12:51 +0200, Nicholas Mc Guire wrote: > > >> Converting milliseconds to jiffies by "val * HZ / 1000" is technically > > >> is not a clean solution as it does not handle all corner cases correctly. > > >> By changing the conversion to use msecs_to_jiffies(val) conversion is > > >> correct in all cases. > > >> > > >> in the current code: > > >> mod_timer(&self->rx_defer_timer, jiffies + (10 * HZ / 1000)); > > >> for HZ < 100 (e.g. CONFIG_HZ == 64|32 in alpha) this effectively results > > >> in no delay at all. > > > [] > > >> diff --git a/drivers/net/irda/irda-usb.c b/drivers/net/irda/irda-usb.c > > > [] > > >> @@ -848,7 +848,9 @@ static void irda_usb_receive(struct urb *urb) > > >> * Jean II */ > > >> self->rx_defer_timer.function = irda_usb_rx_defer_expired; > > >> self->rx_defer_timer.data = (unsigned long) urb; > > >> - mod_timer(&self->rx_defer_timer, jiffies + (10 * HZ / 1000)); > > >> + mod_timer(&self->rx_defer_timer, > > >> + jiffies + (msecs_to_jiffies(10))); > > > > > > The unnecessary () around msecs_to_jiffies could be removed. > > The other thing that could be done is to use > max(1ul, msecs_to_jiffies()) > so that there's always some delay even if HZ <= 50 > I may be mistaken, but I am quite sure that msecs_to_jiffies() always returns at least 1 in such situations. Otherwise there would be lots of converstions to 0 in the kernel. Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/