From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754139Ab1IWRRO (ORCPT ); Fri, 23 Sep 2011 13:17:14 -0400 Received: from mail-fx0-f46.google.com ([209.85.161.46]:35944 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753772Ab1IWRRJ convert rfc822-to-8bit (ORCPT ); Fri, 23 Sep 2011 13:17:09 -0400 MIME-Version: 1.0 In-Reply-To: <4E7C9393.7030804@itanic.dy.fi> References: <4E7C9393.7030804@itanic.dy.fi> Date: Fri, 23 Sep 2011 10:17:07 -0700 Message-ID: Subject: Re: eMMC low write speed From: Praveen G K To: Timo Kokkonen Cc: Qiang LIU , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 23, 2011 at 7:11 AM, Timo Kokkonen wrote: > On 09/23/11 06:03, Praveen G K wrote: >> Hi Qiang, >> >> >> On Thu, Sep 22, 2011 at 7:16 PM, Qiang LIU wrote: >>> Hi, >>> >>> I suggest you change another eMMC card or try SDHC card. It seems like >>> a card issue. >> >> Thanks for the response.  So, do you think this has nothing to do with >> the caching or any such issues, since it is only every 63rd and 64th >> transfer causing this issue? > > It is very much possible that the card itself does something internally > on every 63rd or 64th transfer. Such as wear leveling management on the > nand or perhaps some copy-on-write operations if the transfers are not > taking place in contiguous blocks. The way I am testing it is as follows time -p dd if=/dev/zero of=/dev/mmcblk0 bs=512k count=10 (I have tried different values for count) When I especially try for count = 10, I see the request completed in 0.25 seconds or as high as 1 second. When it is 0.25 s, the speed is 20MBps, and when it is 1s, the speed is 5MBps. So, I am not sure whether I am missing something here. I am using the Sandisk SDIN5C1-4G card for testing. Any other card of the same family, I see only a speed of 5MBps. > As suggested above, you could try with another eMMC or SDCH card if it > makes a different (if possible). > > -Timo >