From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nikhilesh Reddy Subject: Using Cache barriers in lieu of REQ_FLUSH | REQ_FUA for emmc 5.1 (jdec spec JESD84-B51) Date: Tue, 15 Sep 2015 16:17:46 -0700 Message-ID: <55F8A71A.3030001@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit To: Theodore Ts'o , linux-ext4@vger.kernel.org Return-path: Received: from smtp.codeaurora.org ([198.145.29.96]:41189 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750764AbbIOXRy (ORCPT ); Tue, 15 Sep 2015 19:17:54 -0400 Sender: linux-ext4-owner@vger.kernel.org List-ID: Hi The eMMC 5.1 spec defines cache "barrier" capability of the eMMC device as defined in JESD84-B51 I was wondering if there were any downsides to replacing the WRITE_FLUSH_FUA with the cache barrier? I understand that REQ_FLUSH is used to ensure that the current cache be flushed to prevent any reordering but I dont seem to be clear on why REQ_FUA is used. Can someone please help me understand this part? But as far as I understand it ... the cache barriers can be used to replace all the flush requests. Please let me know if there is any downside to this ? I know there there was a big decision in 2010 https://lwn.net/Articles/400541/ and http://lwn.net/Articles/399148/ to remove the software based barrier support... but with the hardware supporting "barriers" is there a downside to using them to replace the flushes? -- Thanks Nikhilesh Reddy Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.