From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from wolverine01.qualcomm.com ([199.106.114.254]:60469 "EHLO wolverine01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751877Ab0LVW2J (ORCPT ); Wed, 22 Dec 2010 17:28:09 -0500 Message-ID: <4D127B78.7060707@codeaurora.org> Date: Wed, 22 Dec 2010 14:28:08 -0800 From: Abhijeet Dharmapurikar MIME-Version: 1.0 Subject: release_console_sem() and disabling interrupts Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-arm-msm-owner@vger.kernel.org List-ID: To: linux-kernel@vger.kernel.org Cc: Andrew Morton , Namhyung Kim , Kees Cook , James Morris , Ingo Molnar , linux-arm-msm@vger.kernel.org, smuckle@codeaurora.org release_console_sem() disables interrupts while it calls upon the console drivers to dump the pending characters. This disabling of interrupt is delaying the handling of interrupts leading to weird latencies and bugs. The specific scenario is while resuming, the __log_buf has accumulated around 11,000 bytes of characters and resume_console takes for ever to send them out. On my system with serial running at 115200 baud it takes almost a second to flush 11,000 bytes. I was thinking about limiting the characters to say N bytes and before the next set of N bytes is sent, we enable interrupts and do the spin_lock_irqsave again. Basically spin in the for ( ; ; ) loop until all the outstanding bytes are sent in sets of N bytes. This issue has been brought up many times earlier - http://www.webservertalk.com/archive242-2006-6-1537307.html http://www.webservertalk.com/archive242-2007-11-2129981.html One reason I gather is that we want to prevent interrupts from printing unorderly stuff in the __log_buf. But dont interrupts get the spin_lock(&logbuf_lock) and then update the log_[end/start], con_start etc? If so we wont see unorderly prints in the __log_buf, the spin_lock protects those pointers. Would like ask if limiting the number of characters per loop in release_console_sem() is a good idea. Thanks Abhijeet Sent by an Employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc is a member of code aurora forum.