Date: Fri, 26 May 2006 20:03:22 +0000 From: John Birrell <jb@what-creek.com> To: Joseph Koshy <joseph.koshy@gmail.com> Cc: current@freebsd.org Subject: Re: DTrace for FreeBSD - Status Update Message-ID: <20060526200322.GC34554@what-creek.com> In-Reply-To: <84dead720605260818t7460cd6dp5de7311a1b5edc28@mail.gmail.com> References: <20060525065510.GA20475@what-creek.com> <m264jt2mjw.wl%gnn@neville-neil.com> <84dead720605260818t7460cd6dp5de7311a1b5edc28@mail.gmail.com>
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On Fri, May 26, 2006 at 08:48:21PM +0530, Joseph Koshy wrote: > >But, I have a naive question. Should this be integrated in > >some way with the hwpmc work of Joseph Koshy since I think it > >could be useful for DTRace to get information from the CPU as > >well. > > Disclaimer: I've only just started reading about DTrace. > > There appear to be two ways to integrate hwpmc and DTrace: > > - Augment the D virtual machine with a primitive that can > read PMC values (e.g.- using RDPMC or RDMSR instructions > on x86 CPUs). Make this primitive available > to scripts for allocating and reading from PMCs (say > a "pmcread()" builtin function). > > This approach would work well with counting mode PMCs > (both process and system-mode counting PMCs) and would > allow PMCs to be read at arbitrary points of time. > > We'll need a way of allocating system-wide & process-mode > PMCs; this could be done in userland (in dtrace(8)). > > - hwpmc(4) can be augmented to be a 'DTrace provider' > allowing D scripts to be run, say when a PC sample is > recorded. Before modifying the virtual machine in FreeBSD's DTrace port, it would be best to discuss this in the "DTrace Community" <http://www.opensolaris.org/jive/forum.jspa?forumID=7>; The Sun guys will guide us on which way they think is appropriate. -- John Birrell
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