Date: Thu, 23 Jun 2011 12:53:43 +0200 From: Marius Strobl <marius@alchemy.franken.de> To: Peter Jeremy <peter.jeremy@alcatel-lucent.com> Cc: freebsd-sparc64@freebsd.org Subject: Re: SPARC64 context switching oddities Message-ID: <20110623105343.GA38525@alchemy.franken.de> In-Reply-To: <20110623053051.GL65891@pjdesk.au.alcatel-lucent.com> References: <20110623053051.GL65891@pjdesk.au.alcatel-lucent.com>
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On Thu, Jun 23, 2011 at 03:30:51PM +1000, Peter Jeremy wrote: > I have a tool that measures the rate at which a single-byte token can > be passed between two processes via a socketpair and have been running > multiple copies of it on an otherwise idle V890 (16-CPU, 64GB RAM > running -current from about a week ago), capturing 'vmstat -s' output. > In the process, I have found several oddities: > > 1) The number of context switches doesn't match my expectations. > See http://i.imgur.com/TyU3j.jpg > It starts out unexpectedly high (~184k switches/sec) and then drops to > an unrealistically low value as the number of processes increases from > 1 to about 20 pairs. It then very slowly increases. Based on one > process writing a token to a second process requiring one context > switch, I would expect the number of context switches to roughly match > the green (based on token passing rate) or blue (based on syscall > rate) lines. > > 2) The transfer rate dips initially then rises to a peak before tailing off. > See http://i.imgur.com/zVcfu.jpg and http://i.imgur.com/DhMmV.jpg > The red line shows the rate reported by the program and the green line > shows the rate estimated from the syscall rate. I would expect a fairly > flat peak from 1 to about 16 pairs (since there are 16 execution threads > available) that then tailed off as scheduler overheads increased > > Can anyone offer an explanation for this behaviour? > I guess you're better off trying to find someone who knows about the schedulers on arch@. Marius
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