Date: Sun, 16 Nov 2003 11:45:45 -0800 (PST) From: Nate Lawson <nate@root.org> To: Luigi Rizzo <rizzo@icir.org> Cc: cvs-src@FreeBSD.org Subject: Re: cvs commit: src/sys/netinet in_var.h ip_fastfwd.c ip_flow.c ip_flow.h ip_input.c ip_output.c src/sys/sys mbuf.h src/sys/conf files src/sys/net if_arcsubr.c if_ef.c if_ethersubr.c if_fddisubr.c if_ Message-ID: <20031116114258.V57495@root.org> In-Reply-To: <20031116003939.A10853@xorpc.icir.org> References: <200311142102.hAEL2Nen073186@repoman.freebsd.org> <3FB593F5.1053E7E2@pipeline.ch><3FB60181.4256A519@pipeline.ch> <20031116003939.A10853@xorpc.icir.org>
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On Sun, 16 Nov 2003, Luigi Rizzo wrote: > On Sun, Nov 16, 2003 at 12:48:14PM +1100, Peter Jeremy wrote: > ... > > >I will try to measure that with more precision. You did have > > >code which was able to record and timestamp events several > > >thousand times per second. Do still have that code somewhere? > > there is some MD code in the RELENG_4 tree, the kernel option > you need is "options KERN_TIMESTAMP" and a description on how > to use it is in sys/i386/include/param.h > > Note that you have to be careful when timing very short sections > of code, because the CPU can execute instruction out of order > so something like > > rdtsc(); > <short section of code> > rdtsc() > > might result in the second timing call being executed before > the section of code in the middle is complete. There is > some nonintuitive instruction (which i now forget) to flush the > execution pipeline which can be used around the section of > code you want to time. cpuid -Nate
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