Date: Tue, 25 Nov 2014 00:59:40 -0700 From: Warner Losh <imp@bsdimp.com> To: Mark R V Murray <mark@grondar.org> Cc: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>, Ian Lepore <ian@FreeBSD.org>, arch@freebsd.org Subject: Re: svn commit: r274739 - head/sys/mips/conf Message-ID: <4DC9E093-C877-40D4-A998-2C94318FECA6@bsdimp.com> In-Reply-To: <B7727BFD-FBEC-4574-8382-7A00AF6D27AF@grondar.org> References: <201411200552.sAK5qnXP063073@svn.freebsd.org> <20141120084832.GE24601@funkthat.com> <AE8F2D30-7F91-4C90-B79A-D99857D8AED8@grondar.org> <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> <F017033A-B761-4435-A7F8-264D2F4662A0@grondar.org> <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> <CC6B67E1-55A2-4952-AB43-5F6C787F629B@grondar.org> <86wq6k9okk.fsf@nine.des.no> <4C2BD093-BEA2-47F9-B575-90342712E9B2@bsdimp.com> <B7727BFD-FBEC-4574-8382-7A00AF6D27AF@grondar.org>
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[-- Attachment #1 --] > On Nov 25, 2014, at 12:57 AM, Mark R V Murray <mark@grondar.org> wrote: > > >> On 24 Nov 2014, at 23:22, Warner Losh <imp@bsdimp.com> wrote: >> >> What’s 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… Maybe there’s some underlying expectation for this function >> that these systems either aren’t providing or can’t provide. > > 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… Warner [-- Attachment #2 --] -----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-----help
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