From owner-freebsd-arch@FreeBSD.ORG Tue Nov 25 07:59:50 2014 Return-Path: Delivered-To: arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id B4126127 for ; Tue, 25 Nov 2014 07:59:50 +0000 (UTC) Received: from mail-pd0-f180.google.com (mail-pd0-f180.google.com [209.85.192.180]) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 78326E43 for ; Tue, 25 Nov 2014 07:59:50 +0000 (UTC) Received: by mail-pd0-f180.google.com with SMTP id p10so58969pdj.39 for ; Mon, 24 Nov 2014 23:59:44 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:sender:subject:mime-version:content-type:from :in-reply-to:date:cc:message-id:references:to; bh=wMYIC6NtnTXuINCbwMBDH3Y51ThH1vNs7znWpyHJ4xQ=; b=kXc/3h+R1ckAdDP8MD2fytqSAhpRFbMmyrpEMnBY6Yw6cm3ASBKYQUR9o5exYZ39qE X/9v4YsSkRNhFJ2cx8t9rqB7ojJE9NaqrrX3+J+vnbzFruqX3K9ek59V++vouVYo5dM8 vD+GbQ4eHsTqLCsHhE7wSaAlC4xQTlU5behM+nofxapK+2D5bEFeEp0JYdqqSwSqvvBy 4M49dVZM/Wu4GMrOCbSkhGkXQ39t7EsvK2AQt2quLMyUDxLkmpfWDzPS/MnLCJppU5sv 2GButlijgpsDxFXk77s269HLwvz9RwLEzCStCi101jpmaL+FXqCdVkVtj3EZ+feVVETu Kifg== X-Gm-Message-State: ALoCoQmfH/Hjgm7iBJHMV2exFxKU4iw5gnZvCN4t+HD9jIfQ3W1NchPtA/0TAa3JZTTc6ZWfajhy X-Received: by 10.70.100.170 with SMTP id ez10mr40395387pdb.73.1416902384061; Mon, 24 Nov 2014 23:59:44 -0800 (PST) Received: from [10.64.26.139] ([69.53.236.236]) by mx.google.com with ESMTPSA id pj5sm652715pdb.65.2014.11.24.23.59.42 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 24 Nov 2014 23:59:43 -0800 (PST) Sender: Warner Losh Subject: Re: svn commit: r274739 - head/sys/mips/conf Mime-Version: 1.0 (Mac OS X Mail 8.1 \(1993\)) Content-Type: multipart/signed; boundary="Apple-Mail=_194AE083-21C7-43E7-BD0E-386E833EAC1E"; protocol="application/pgp-signature"; micalg=pgp-sha512 X-Pgp-Agent: GPGMail 2.5b2 From: Warner Losh In-Reply-To: Date: Tue, 25 Nov 2014 00:59:40 -0700 Message-Id: <4DC9E093-C877-40D4-A998-2C94318FECA6@bsdimp.com> 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> To: Mark R V Murray X-Mailer: Apple Mail (2.1993) 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 07:59:50 -0000 --Apple-Mail=_194AE083-21C7-43E7-BD0E-386E833EAC1E Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > 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. 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 Warner --Apple-Mail=_194AE083-21C7-43E7-BD0E-386E833EAC1E Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJUdDbtAAoJEGwc0Sh9sBEArCkP+wf+vA3VfAeJdNzdxB36gH8V XTfdstgV6flM723BaurBHy187uqHhZP4GMVhvdIRvIKO7xYYOPm6Vk2bxZZ5Nexv 5mDN2bgOWiPMB0h68sm8nmsno2U/0tcbK+DWEVBwDIsMB/IYYTByl98nH90oyVDk lgVUeM5SQ0FRTyH1VRL5txRTHE1WrvC7jtCyLTjIHCnHMYSAUbd0R++EYVmSvWHV 1aANPADhrDX9DWnhytw/Dxj4C/6FA6dWNRcCc/BW9eZUrUOneo/LUX0EXNE5xnTu SaUrZQxXThDVgCbExtB7OPKJ9/liigtcQMxR0MNoJaNlqmNwZW6xiVKSEXAVCKNR 7gUQFG29k2eQrB/XYbAF8xkSWbZXyHYzXpUHpTQd6CdHgRHfw4AtppZF+w0YvSLn zINTGEBH8EQEf90Y+e7wZnhC01OCPYFk5LH/4p32IbCYXkkMKB/iMbbdMXZQ0Hnu E59rl0M0UWRWQksdD4YwiZegynk1fyjJR2IcP8Aa8CIe3xwlniuMF59RLrqFy21S Qj6j9ysH9QGwvAt1qXRj3lzznly4nLLfvU9RkhAydWOX9DH8NdViL/uy65l/u12T Xe0yBWp9fsE+NC9fPvA9haxsYTMpyvBF1gIxk0GDBfrX9m7hKEODnN1Tkk9UZY/r 6KA8jzwxFNiP9CFrZf45 =ffoI -----END PGP SIGNATURE----- --Apple-Mail=_194AE083-21C7-43E7-BD0E-386E833EAC1E--