From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vk0-f53.google.com ([209.85.213.53]:33616 "EHLO mail-vk0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750766AbdCYI3g (ORCPT ); Sat, 25 Mar 2017 04:29:36 -0400 Received: by mail-vk0-f53.google.com with SMTP id d188so10615913vka.0 for ; Sat, 25 Mar 2017 01:29:35 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: From: Sitsofe Wheeler Date: Sat, 25 Mar 2017 08:29:04 +0000 Message-ID: Subject: Re: Clat min zero on Randread? Content-Type: text/plain; charset=UTF-8 Sender: fio-owner@vger.kernel.org List-Id: fio@vger.kernel.org To: Tarek Cc: "fio@vger.kernel.org" Hi, I don't know why the minimum clat is 0 usec (you might be able to investigate further by using blktrace on the device to see how much that disagrees with fio) but why do you believe that scenario happened on the exact same I/O(s) that had a 0 usec slat time? Do you have additional logs showing that was the case? On 24 March 2017 at 17:39, Tarek wrote: > Clat min is zero on a random read, how is that possible when NAND tR > spec is 20-60uS? Also isn't lat = slat + clat, 1 + 0 != 84 > > fio-2.15 > Starting 80 threads > > random-100r-0w_4k_qd1_jobs_16: (groupid=0, jobs=16): err= 0: > pid=22233: Tue Feb 21 15:41:33 2017 > Description : [Random R/W 100/0 QD1 BLK 4k Jobs 16] > read : io=1045.5GB, bw=609017KB/s, iops=152254, runt=1800001msec > slat (usec): min=1, max=6583, avg= 2.06, stdev= 1.01 > clat (usec): min=0, max=8728, avg=102.38, stdev=21.43 > lat (usec): min=84, max=8730, avg=104.52, stdev=21.45 > clat percentiles (usec): > | 1.00th=[ 85], 5.00th=[ 86], 10.00th=[ 87], 20.00th=[ 89], > | 30.00th=[ 91], 40.00th=[ 98], 50.00th=[ 101], 60.00th=[ 102], > | 70.00th=[ 104], 80.00th=[ 106], 90.00th=[ 116], 95.00th=[ 143], > | 99.00th=[ 175], 99.50th=[ 185], 99.90th=[ 225], 99.95th=[ 239], > | 99.99th=[ 270] > > > Fio Config: > thread > bs=4k > ioengine=libaio > direct=1 > buffered=0 > log_avg_msec=1000 > group_reporting=1 > rw=randread > numjobs=16 > iodepth=1 > time_based > runtime=1800 > refill_buffers > norandommap > filename=/dev/nvme0n1 -- Sitsofe | http://sucs.org/~sits/