From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f50.google.com ([74.125.82.50]:52231 "EHLO mail-wm0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751269AbeCPVRD (ORCPT ); Fri, 16 Mar 2018 17:17:03 -0400 Received: by mail-wm0-f50.google.com with SMTP id t3so5489338wmc.2 for ; Fri, 16 Mar 2018 14:17:02 -0700 (PDT) From: Michael Green Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Mime-Version: 1.0 (Mac OS X Mail 10.3 \(3273\)) Subject: Re: random_generator=lfsr overhead with more disks? Date: Fri, 16 Mar 2018 17:16:56 -0400 References: <9FD577EB-5F83-4AB3-9FBA-704094437C15@gmail.com> In-Reply-To: Message-Id: Sender: fio-owner@vger.kernel.org List-Id: fio@vger.kernel.org To: Jeff Furlong , "fio@vger.kernel.org" > -How does the cpu utilization look compared between the lfsr and = default tausworthe generators? Is the cpu util actually higher on lfsr? = =20 It is actually less when using LFSR with 16 volumes: Without LFSR (CPU utilization is 5th column): [root@sm28 ~]# ps -eLo ppid,pid,pri,psr,pcpu,stat,wchan:14,comm | grep = fio PPID PID PRI PSR %CPU STAT WCHAN COMMAND 2239 24684 19 0 0.7 Sl+ hrtimer_nanosl fio 2239 24684 19 0 0.2 Sl+ futex_wait_que fio 2239 24684 19 3 60.4 Rl+ - fio 2239 24684 19 6 60.5 Sl+ - fio 2239 24684 19 1 61.2 Rl+ - fio 2239 24684 19 23 62.5 Sl+ - fio 2239 24684 19 7 60.6 Rl+ - fio 2239 24684 19 18 61.0 Rl+ - fio 2239 24684 19 16 61.0 Rl+ - fio 2239 24684 19 4 62.0 Rl+ - fio With LFSR: [root@sm28 ~]# ps -eLo ppid,pid,pri,psr,pcpu,stat,wchan:14,comm | grep = fio 2239 25589 19 20 2.7 Sl+ hrtimer_nanosl fio 2239 25589 19 25 0.3 Sl+ futex_wait_que fio 2239 25589 19 16 80.1 Rl+ - fio 2239 25589 19 22 78.0 Rl+ - fio 2239 25589 19 5 82.6 Rl+ - fio 2239 25589 19 4 78.0 Rl+ - fio 2239 25589 19 18 82.7 Rl+ - fio 2239 25589 19 17 80.7 Sl+ 14051005663345 fio 2239 25589 19 23 76.6 Sl+ - fio 2239 25589 19 0 77.6 Rl+ - fio But almost the same with 1 volume: Without LFSR [root@sm28 ~]# ps -eLo ppid,pid,pri,psr,pcpu,stat,wchan:14,comm | grep = fio 2239 27559 19 7 4.0 Sl+ hrtimer_nanosl fio 2239 27559 19 2 0.0 Sl+ futex_wait_que fio 2239 27559 19 18 79.4 Rl+ - fio 2239 27559 19 17 79.0 Rl+ - fio 2239 27559 19 6 78.6 Rl+ - fio 2239 27559 19 5 77.6 Rl+ - fio 2239 27559 19 23 82.6 Rl+ - fio 2239 27559 19 3 77.4 Rl+ - fio 2239 27559 19 4 77.1 Sl+ - fio 2239 27559 19 16 75.9 Rl+ - fio With LFSR: [root@sm28 ~]# ps -eLo ppid,pid,pri,psr,pcpu,stat,wchan:14,comm | grep = fio 2239 27174 19 20 2.0 Sl+ hrtimer_nanosl fio 2239 27174 19 25 0.0 Sl+ futex_wait_que fio 2239 27174 19 16 80.0 Rl+ - fio 2239 27174 19 6 78.4 Rl+ - fio 2239 27174 19 3 77.5 Rl+ - fio 2239 27174 19 5 76.4 Sl+ - fio 2239 27174 19 19 77.1 Rl+ - fio 2239 27174 19 4 76.4 Rl+ - fio 2239 27174 19 7 77.0 Rl+ - fio 2239 27174 19 1 75.8 Rl+ - fio > -Does a runtime of 2 minutes collect enough data points to assess the = condition? What happens if you extend the runtime? Yes, it does. Shortening the test to 20 sec or extending to 10 min, = doesn=E2=80=99t change a thing.