From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rolf Fokkens Subject: Re: bcache_writebac task 100% CPU Date: Tue, 20 May 2014 21:38:35 +0200 Message-ID: <537BAF3B.2020607@rolffokkens.nl> References: <53786E02.8060300@rolffokkens.nl> <20140519165550.GD2276@kmo> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ee0-f42.google.com ([74.125.83.42]:38667 "EHLO mail-ee0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750807AbaETTij (ORCPT ); Tue, 20 May 2014 15:38:39 -0400 Received: by mail-ee0-f42.google.com with SMTP id d49so876180eek.15 for ; Tue, 20 May 2014 12:38:37 -0700 (PDT) In-Reply-To: <20140519165550.GD2276@kmo> Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: Kent Overstreet Cc: linux-bcache@vger.kernel.org On 05/19/2014 06:55 PM, Kent Overstreet wrote: > ...Changing it back to 25% doesn't do anything? _that_ is odd... > > Can you send me the output of writeback_rate_debug? Check it once before you've > done anything, when things are working normally (after a fresh boot when > writeback_percent is nonzero, probably), then grab it again after you've set > writeback_percent to 0 and then back to 25, when it's still spinning. I collected the requested data by logging both writeback_percent and writeback_rate_debug every second. Every second also the cumulative CPU usage of the bcache_writebac task is logged (as shown by ps -efw), showing that the task is burning CPU cycles. Both the collecting script and the log file can be found here: https://bugzilla.kernel.org/show_bug.cgi?id=76391 > Also, what kernel are you running? As mentioned before, the kernel is Fedora kernel kernel-3.14.4-200.fc20.x86_64