Date: Tue, 7 Feb 2006 17:46:34 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-current@freebsd.org, Andre Oppermann <andre@freebsd.org> Subject: Re: machdep.cpu_idle_hlt and SMP perf? Message-ID: <17385.9034.309439.331530@grasshopper.cs.duke.edu> In-Reply-To: <200602071730.53881.jhb@freebsd.org> References: <17379.56708.421007.613310@grasshopper.cs.duke.edu> <200602071037.05314.jhb@freebsd.org> <17385.7187.845964.182297@grasshopper.cs.duke.edu> <200602071730.53881.jhb@freebsd.org>
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John Baldwin writes: > On Tuesday 07 February 2006 17:15, Andrew Gallatin wrote: > > John Baldwin writes: > > > On Monday 06 February 2006 17:37, Andrew Gallatin wrote: > > > > John Baldwin writes: > > > > > On Monday 06 February 2006 14:46, Andrew Gallatin wrote: > > > > > > Andre Oppermann writes: > > > > > > > Andrew Gallatin wrote: > > > > > > > > Why dooes machdep.cpu_idle_hlt=1 drop my 10GbE network rx > > > > > > > > performance by a considerable amount (7.5Gbs -> 5.5Gbs)? > > > > > > > > > > You may be seeing problems because it might simply take a while for > > > > > the CPU to wake up from HLT when an interrupt comes in. The 4BSD > > > > > scheduler tries to do IPIs to wakeup any sleeping CPUs when it > > > > > schedules a new thread, but that would add higher latency for > > > > > ithreads than just preempting directly to the ithread. Oh, you > > > > > have to turn that on, it's off by default > > > > > (kern.sched.ipiwakeup.enabled=1). > > > > > > > > Hmm.. It seems to be on by default. Unfortunately, it does not seem > > > > to help. > > > > > > I'm not sure. > > > > One thing which really helps is disabling preemption. If I do that, > > I get 7.7Gb/sec with machdep.cpu_idle_hlt=1. This is slightly better > > than machdep.cpu_idle_hlt=0 and no PREEMPTION. > > > > BTW, net.isr.direct=1 in all testing. > > Do you have very little userland activity in this test? Essentially none. netserver just sits in a loop, reading from the socket and throwing the data away. Drew
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