Date: Fri, 20 Mar 2015 20:46:56 -0400 From: Mike Tancsa <mike@sentex.net> To: Konstantin Belousov <kostikbel@gmail.com>, d@delphij.net Cc: John-Mark Gurney <jmg@funkthat.com>, FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org>, John Baldwin <jhb@freebsd.org> Subject: Re: RELENG_10 performance regression (was Re: 35-40% performance drop releng9 vs releng10 openvpn Message-ID: <550CBF80.6030809@sentex.net> In-Reply-To: <20150321001559.GB2379@kib.kiev.ua> References: <5506250A.2000506@sentex.net> <20150316132055.GQ32288@funkthat.com> <5509D6C6.4050204@sentex.net> <20150318211457.GL51048@funkthat.com> <550B6950.8060806@sentex.net> <550C5AAF.9060502@sentex.net> <550C8AEE.4090408@sentex.net> <550CB306.7030405@delphij.net> <20150321001559.GB2379@kib.kiev.ua>
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On 3/20/2015 8:15 PM, Konstantin Belousov wrote: >> >> For the purpose of devfs, does it make sense to bump timestamps like >> normal filesystems for each read/write operation? Looks like Mac OS X >> will bump timestamps for each operation but Debian don't. > > First question is, what timecounter hardware is used. I would accept > some slowdown from hardware like HPET, but it is indeed surprising > if caused by TSC. > > David Wolfskill suggested trying the problem commit with vfs.timestamp_precision=0 and it does indeed restore performance to what it was. The raw dtrace files are available and FlameGraphs can all be found at http://tancsa.com/time/ ---Mike -- ------------------- Mike Tancsa, tel +1 519 651 3400 Sentex Communications, mike@sentex.net Providing Internet services since 1994 www.sentex.net Cambridge, Ontario Canada http://www.tancsa.com/
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