From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <56D91110.8080203@vlnb.net> Date: Thu, 03 Mar 2016 20:37:36 -0800 From: Vladislav Bolkhovitin MIME-Version: 1.0 Subject: Re: Fio high IOPS measurement mistake References: <56D525E1.6010407@vlnb.net> <56D66B1C.6050506@vlnb.net> <56D7A97F.9080800@vlnb.net> <20160303162037.GD22164@kernel.dk> In-Reply-To: <20160303162037.GD22164@kernel.dk> Content-Type: text/plain; charset=windows-1251 Content-Transfer-Encoding: 7bit To: Jens Axboe , Sitsofe Wheeler Cc: "fio@vger.kernel.org" List-ID: Jens Axboe wrote on 03/03/2016 08:20 AM: > On Thu, Mar 03 2016, Sitsofe Wheeler wrote: >> On 3 March 2016 at 03:03, Vladislav Bolkhovitin wrote: >>> For those who asked about perf profiling, it remained the same as before with the CPU >>> consumption is all about timekeeping and memset: >>> >>> - 55.74% fio fio [.] clock_thread_fn >>> clock_thread_fn >> >> Perhaps this is what is already included above but could you use the >> -g option on perf to collect it into a call-graph and post the top >> results? > > The above looks like a side effect of using gtod_cpu, it'll burn one > core. For the original poster - did you verify whether using gtod_cpu > was faster than using the CPU clock source in each CPU? Yes, I had verified it and mentioned in one of my reports. It slightly decreased the IOPS. I guess, it's a locking contention somewhere. Thanks, Vlad