From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: Re: [PATCH] tty: prevent unnecessary work queue lock checking on flip buffer copy Date: Thu, 20 Sep 2012 17:33:05 +0100 Message-ID: <20120920173305.15ea580a@bob.linux.org.uk> References: <1348149762-4596-1-git-send-email-meltedpianoman@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from mga09.intel.com ([134.134.136.24]:51845 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755291Ab2ITQO7 (ORCPT ); Thu, 20 Sep 2012 12:14:59 -0400 In-Reply-To: <1348149762-4596-1-git-send-email-meltedpianoman@gmail.com> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Ivo Sieben Cc: Greg KH , linux-serial@vger.kernel.org, RT > This prevents unnecessary spin lock/unlock on the workqueue spin lock > that can cause additional scheduling overhead on a PREEMPT_RT system. > On a 240 MHz AT91SAM9261 processor setup this fixes about 100us of > scheduling overhead on the TTY read call. This seems reasonable, but given its also relevant for upstream it would be nice to get it without the ifdef in upstream. The corner case is when the tty->low_latency flag is flipped but the drivers should handle that gracefully and if not we should fix them so you can get your 100uS. Alan