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Message-ID: <Pine.LNX.4.64.0810311119510.7072@wrl-59.cs.helsinki.fi> Date: Fri, 31 Oct 2008 11:40:16 +0200 (EET) From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi> To: David Miller <davem@...emloft.net> cc: shemminger@...tta.com, zbr@...emap.net, rjw@...k.pl, mingo@...e.hu, s0mbre@...rvice.net.ru, a.p.zijlstra@...llo.nl, LKML <linux-kernel@...r.kernel.org>, Netdev <netdev@...r.kernel.org>, efault@....de, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [tbench regression fixes]: digging out smelly deadmen. On Fri, 31 Oct 2008, David Miller wrote: > 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. Let me remind that it is just a single process, so no ping-pong & other lock related cache effects should play any significant role here, no? (I'm no expert though :-)). One thing I didn't mention earlier, is that I also turned on tcp_tw_recycle to get the binding to work without giving -ESOMETHING very early (also did some, possibly meaningless things, like drop_caches before each test run, might be significant only because of the test harness cause minor variantions). I intend to try w/o binding of the client end but I guess I might again get more variation between different test runs. -- i.
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