Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752031AbZJPErx (ORCPT ); Fri, 16 Oct 2009 00:47:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751450AbZJPErw (ORCPT ); Fri, 16 Oct 2009 00:47:52 -0400 Received: from gate.crashing.org ([63.228.1.57]:57318 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751823AbZJPErv (ORCPT ); Fri, 16 Oct 2009 00:47:51 -0400 Subject: Re: [PATCH] hvc_console: returning 0 from put_chars is not an error From: Benjamin Herrenschmidt To: Scott Wood Cc: Christian Borntraeger , linuxppc-dev@ozlabs.org, brueckner@linux.vnet.ibm.com, Timur Tabi , Alan Cox , Linux Kernel Mailing List In-Reply-To: <4AD770A9.6070509@freescale.com> References: <1255557226-4403-1-git-send-email-timur@freescale.com> <200910151305.47100.borntraeger@de.ibm.com> <20091015160906.GA3730@loki.buserror.net> <200910152041.26646.borntraeger@de.ibm.com> <4AD770A9.6070509@freescale.com> Content-Type: text/plain; charset="UTF-8" Date: Fri, 16 Oct 2009 15:46:45 +1100 Message-Id: <1255668405.19032.13.camel@pasglop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1383 Lines: 30 On Thu, 2009-10-15 at 13:57 -0500, Scott Wood wrote: > I'd say the dropping approach is quite undesirable (significant > potential for output loss unless the buffer is huge), unless there's > simply no way to safely spin. Hopefully there are no such backends, but > if there are perhaps we can have them return some special code to > indicate that. Should never spin. Best is to keep a copy in the upper layer of the pending data and throttle (not accept further data from tty layer) until we have managed to flush out that "pending" buffer. > > If we just busy loop, it actually does not matter how we let hvc_console react > > on 0, as long as we adopt all backends to use that interface consistent. > > > > On the other hand, backends might want to do special magic on congestion so I > > personally tend to let the backend loop instead of hvc_console. But I am really > > not sure. > > Doing it in the backend requires the backend to know whether it's being > called for printk or for user I/O. In the latter case, we don't want to > spin, but rather wait for an IRQ (or poll with a timer if there's no IRQ). Ben. -- 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/