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Date: Fri, 31 Oct 2008 00:52:19 -0700 (PDT) From: David Miller <davem@...emloft.net> To: ilpo.jarvinen@...sinki.fi Cc: shemminger@...tta.com, zbr@...emap.net, rjw@...k.pl, mingo@...e.hu, s0mbre@...rvice.net.ru, a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, efault@....de, akpm@...ux-foundation.org Subject: Re: [tbench regression fixes]: digging out smelly deadmen. From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi> Date: Thu, 30 Oct 2008 21:01:19 +0200 (EET) > On Thu, 30 Oct 2008, Stephen Hemminger wrote: > > > Has anyone looked into the impact of port randomization on this benchmark. > > If it is generating lots of sockets quickly there could be an impact: > > * port randomization causes available port space to get filled non-uniformly > > and what was once a linear scan may have to walk over existing ports. > > (This could be improved by a hint bitmap) > > > > * port randomization adds at least one modulus operation per socket > > creation. This could be optimized by using a loop instead. > > I did something with AIM9's tcp_test recently (1-2 days ago depending on > how one calculates that so didn't yet have time summarize the details in > the AIM9 thread) by deterministicly binding in userspace and got much more > sensible numbers than with randomized ports (2-4%/5-7% vs 25% variation > some difference in variation in different kernel versions even with > deterministic binding). Also, I'm still to actually oprofile and bisect > the remaining ~4% regression (around 20% was reported by Christoph). For > oprofiling I might have to change aim9 to do predefined number of loops > instead of a deadline to get more consistent view on changes in per func > runtime. Yes, it looks like port selection cache and locking effects are a very real issue. Good find. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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