From owner-freebsd-arch@FreeBSD.ORG Tue Nov 25 08:32:50 2014 Return-Path: Delivered-To: arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 5253F9AD; Tue, 25 Nov 2014 08:32:50 +0000 (UTC) Received: from gromit.grondar.org (grandfather.grondar.org [93.89.92.32]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 0FA74278; Tue, 25 Nov 2014 08:32:48 +0000 (UTC) Received: from [2001:470:9174:1:a022:fe58:8d38:bb1f] by gromit.grondar.org with esmtpsa (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.84 (FreeBSD)) (envelope-from ) id 1XtBX0-0003KU-Ik; Tue, 25 Nov 2014 08:31:32 +0000 Subject: Re: svn commit: r274739 - head/sys/mips/conf Mime-Version: 1.0 (Mac OS X Mail 8.1 \(1993\)) Content-Type: text/plain; charset=utf-8 From: Mark R V Murray In-Reply-To: <4DC9E093-C877-40D4-A998-2C94318FECA6@bsdimp.com> Date: Tue, 25 Nov 2014 08:31:29 +0000 Content-Transfer-Encoding: quoted-printable Message-Id: References: <201411200552.sAK5qnXP063073@svn.freebsd.org> <20141120084832.GE24601@funkthat.com> <20141121092245.GI99957@funkthat.com> <1416582989.1147.250.camel@revolution.hippie.lan> <026FEB8A-CA8C-472F-A8E4-DA3D0AC44B34@grondar.org> <1416596266.1147.290.camel@revolution.hippie.lan> <1416598889.1147.297.camel@revolution.hippie.lan> <86egsvueqk.fsf@nine.des.no> <1416691274.1147.339.camel@revolution.hippie.lan> <398A380D-49AF-480C-8842-8835F81EF641@grondar.org> <1416806894.1147.362.camel@revolution.hippie.lan> <18B8A926-59C0-49B4-ADA3-A11688609852@grondar.org> <1416841268.1147.386.camel@revolution.hippie.lan> <86wq6k9okk.fsf@nine.des.no> <4C2BD093-BEA2-47F9-B575-90342712E9B2@bsdimp.com> <4DC9E093-C877-40D4-A998-2C94318FECA6@bsdimp.com> To: Warner Losh X-Mailer: Apple Mail (2.1993) X-SA-Score: -1.0 Cc: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= , Ian Lepore , arch@freebsd.org X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 25 Nov 2014 08:32:50 -0000 > On 25 Nov 2014, at 07:59, Warner Losh wrote: >=20 >=20 >> On Nov 25, 2014, at 12:57 AM, Mark R V Murray = wrote: >>=20 >>=20 >>> On 24 Nov 2014, at 23:22, Warner Losh wrote: >>>=20 >>> What=E2=80=99s the minimum specs required for get_cyclecount()? Not = all of the >>> boxes that Ian was posting about have high-resolution time-keeping = counters >>> in hardware=E2=80=A6 Maybe there=E2=80=99s some underlying = expectation for this function >>> that these systems either aren=E2=80=99t providing or can=E2=80=99t = provide. >>=20 >> get_cyclecount should be a high-resolution timing counter linear in = time, with a minimum tick no more accurate than a single instruction = execution. In practice we take what we can get. It is used to measure = hopefully chaotic events in order to obtain environmental entropy. >=20 > So right. armv6 and mips have something akin to that, but IIRC, not = all arm v4/5 boxes can do much better than microseconds=E2=80=A6 That=E2=80=99s my understanding. I still don=E2=80=99t get the massive = differences; they should be tiny. M --=20 Mark R V Murray