Date: Tue, 7 Jun 2005 13:55:53 +0300 From: Laszlo Vitos <vitos.laszlo@gmail.com> To: Bruce Evans <bde@zeta.org.au> Cc: freebsd-amd64@freebsd.org Subject: Re: top showing incorrect CPU and WCPU on amd64? Message-ID: <200506071355.53607.vitos.laszlo@gmail.com> In-Reply-To: <20050604162348.V5146@delplex.bde.org> References: <200506030943.40215.vitos.laszlo@gmail.com> <20050604162348.V5146@delplex.bde.org>
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On Saturday 04 June 2005 09:34, Bruce Evans wrote: > On Fri, 3 Jun 2005, Laszlo Vitos wrote: > > I observed a strange behavior of top on FreeBSD 5.4-RELEASE on AMD64. It > > seems like the CPU and WCPU columns in top are an average over the > > running time of a process. A small test program confirmed this. It sleeps > > for 2 seconds, then goes over a few iterations of: hogs the cpu in a > > loop, then sleeps again for a few seconds. > > The result: CPU and WCPU never reach 100%, nor 0%, they are > > growing/shrinking in small increments during the process' run time, > > depending on whether the process is sleeping or looping. > > Attached is the test program. Can anyone confirm whether this is the > > expected behavior (and if so, why?)? > > No test program is attached :-). Yes, sorry about that, I don't know why it did not go through. > > I think this is the expected beviour. CPU is a long-term average. Thus > if a process runs for half the time and sleeps for half the time, its CPU > will be about 50%. It won't be exactly 50% since more weight is given > to recent history. WCPU is mostly bogus. It is an attempt to undo the > weighting but not enough history is kept to do this correctly and the > history which is used is close to being garbage. In the meantime I dug into the sched_* sources a bit and realised that indeed, that is the case. Sorry that I didn't look first, but it did not cross my mind that this is actually what the expected behaviour supposed to be. I guess there were a few flame wars about this in the past :) Anyway, thanks for the info, laca
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