From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: Date: Mon, 2 Jun 2008 21:50:53 -0300 From: "Iruata Souza" To: "Fans of the OS Plan 9 from Bell Labs" <9fans@9fans.net> In-Reply-To: <13426df10806021621m7fc4a26fg42b0e8e112837402@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <483D8DBE.4090005@cableone.net> <200805282337.11349.yann.morin.1998@anciens.enib.fr> <20080601151213.GA10795@nibiru.local> <5d375e920806021225w3a98fec0l87ae4499838ae91b@mail.gmail.com> <13426df10806021255y4122f46h34a88ebb8480f29e@mail.gmail.com> <5d375e920806021337m51160c64rf20e0e1f96aca522@mail.gmail.com> <1212445966.4280.1097.camel@work.sfbay.sun.com> <13426df10806021621m7fc4a26fg42b0e8e112837402@mail.gmail.com> Subject: Re: [9fans] crosstool fails on gentoo Topicbox-Message-UUID: b2fbdd6a-ead3-11e9-9d60-3106f5b1d025 On Mon, Jun 2, 2008 at 8:21 PM, ron minnich wrote: > On Mon, Jun 2, 2008 at 4:00 PM, Iruata Souza wrote: > >> I don't have any solaris boxes to play now, but I remember when taking >> a dtrace course - more or less two years ago - that I managed to see >> the performance of a nice machine go down only by setting all it's >> tracing points. I know that this could be considered normal if it >> wasn't for the fact that, with two xterms opened, the one which >> started dtrace, after a series of ^C, had 'transfered' to it the >> command-line history of the other xterm. It was a peculiar situation >> since the instructor was telling us about the non-intrusiveness of the >> tool. >> > > it's worth reading the papers. Dtrace is quite capable. > > But look at the issues. You are taking a piece of code and splicing in > another piece of code. It can get fun. What if someone was running the > code you are splicing (think: SMP). What about time to remove it: make > sure that (a) nobody is running the spliced in code (how do you do > that in the general case) and (b) nobody is trying to run where you > are putting the code back. What if the original code had an INT > instruction? What if it tickled an IRQ? What if code you spliced in > takes a fault? > > Check out the kprobes device in linux to see how nasty it can get. > > At the same time, people delivering software to end users make good > use of dtrace, so it's kind of hard to fault Sun for putting it in > there -- they do have paychecks to hand out. And I expect that lots of > customers demand that it stay in there ... > just like many people, I have made good use of dtrace myself. but the need for a tool like that seems to me one more evidence of the trend in talk about in your first post. in the pile of layers one has to dig to find/fix/rework something, sometimes dtrace seems like the better - or even the only one at hand - thing to deal with it. put short: dtrace-like tools are good but, in general, having the need for it is not. iru