Date: Wed, 14 Jun 2006 10:38:12 -0700 (PDT) From: Danial Thom <danial_thom@yahoo.com> To: Kris Kennaway <kris@obsecurity.org> Cc: Scott Long <scottl@samsco.org>, Robert Watson <rwatson@freebsd.org>, freebsd-performance@freebsd.org, David Xu <davidxu@freebsd.org> Subject: Re: Initial 6.1 questions Message-ID: <20060614173812.60909.qmail@web33311.mail.mud.yahoo.com> In-Reply-To: <20060613210022.GB5267@xor.obsecurity.org>
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--- Kris Kennaway <kris@obsecurity.org> wrote: > On Tue, Jun 13, 2006 at 12:57:38PM -0700, > Danial Thom wrote: > > > Since everyone agrees that the load measuring > > tools aren't all that accurate, what criteria > was > > used to determine that the changes made in 7 > have > > the effect that you think they have had? > > Not by using top(1). vmstat seems to do a > better job of reporting CPU > usage, but still you want to measure what the > system can actually do, > not how accurately it estimates its own > performance. > > Kris > Regarding vmstat: I'm getting the same (obviously wrong) results from vmstat. Which is no usage. I believe I cut and pasted a snippet which showed 6000 ints/second on em with 99.x% idle. It works fine in UP mode, which implies that you aren't accounting properly in SMP mode. Hopefully you (folks) can come to terms with the fact that its broken otherwise it will never be of any use. Regarding testing: My view is that you are making a big mistake if you measure everything at the edge of performance, which is why benchmarks lie and are generally useless. As the bus becomes saturated, and queues become unnaturally large, timings change. You may be measuring how well the system recovers from events that never happen when you just try to "see how much you can do". For example, as the pci bus becomes saturated I/Os take exponentially longer, so you're not really measuring your code. You end up measuring properties which may be very different under normal conditions. And if you try to optimize your code for conditions which rarely if ever occur, you may hose it for normal use (I'm a bit frightened by the 7.0 em changes). "efficiency" is what's important. I want to know how the machine works under normal loads, not when its in constant recovery from overloads. I want to run a realistic load on a machine when I test new code, to see what effect it has on system load. For that I need tools that work. If your machine can push 500Mb/s at 99% load or it can do 492Mb/s at 60% load, my view is that the 492Mb/s system is the better system. In the long run the more efficient systems are the ones that perform better generally. DT __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
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