Date: Thu, 3 Jan 2008 13:46:43 +1100 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Gary Stanley <gary@velocity-servers.net> Cc: josh.carroll@gmail.com, Kris Kennaway <kris@freebsd.org>, freebsd-performance@freebsd.org, Ivan Voras <ivoras@freebsd.org> Subject: Re: mysql scaling questions Message-ID: <20080103134118.G16729@delplex.bde.org> In-Reply-To: <20080102123902.8CB6213C448@mx1.freebsd.org> References: <20071201205609.GA54238@harmless.hu> <20071204130810.GA77186@harmless.hu> <47779AA7.2060801@FreeBSD.org> <20071230132451.GA61295@harmless.hu> <47779EBC.5020900@FreeBSD.org> <20071230134354.GA63555@harmless.hu> <4777A65C.8020406@FreeBSD.org> <20071230141118.GA67574@harmless.hu> <4777AB9C.1010003@FreeBSD.org> <flb6bp$8kq$1@ger.gmane.org> <8cb6106e0801012008q18830aebp906ebfeb3c519e5a@mail.gmail.com> <477B6EB3.50202@FreeBSD.org> <20080102123902.8CB6213C448@mx1.freebsd.org>
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On Wed, 2 Jan 2008, Gary Stanley wrote: > At 06:00 AM 1/2/2008, Kris Kennaway wrote: > >> Per later discussion you will also need to either comment out the syscalls >> that are (might be) being cached by glibc to artificially inflate its >> reported rate, or verify that it is not doing so. > > IIRC linux uses vsyscalls on x86_64, and calling things like gettimeofday() > isn't as expensive as it normally should be.. vsyscalls are similar to > darwins' commpage. How does it implement gettimeofday()'s 1us precision using direct access? I see one way: put the time and other volatiles on an unmapped page, and update the time in the trap handler. With a lot of work, this should be only slightly slower than the gettimeofday() syscall. Bruce
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