Date: Tue, 7 Feb 2006 10:37:03 -0500 From: John Baldwin <jhb@freebsd.org> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: freebsd-current@freebsd.org, Andre Oppermann <andre@freebsd.org> Subject: Re: machdep.cpu_idle_hlt and SMP perf? Message-ID: <200602071037.05314.jhb@freebsd.org> In-Reply-To: <17383.53150.324978.91528@grasshopper.cs.duke.edu> References: <17379.56708.421007.613310@grasshopper.cs.duke.edu> <200602061532.02223.jhb@freebsd.org> <17383.53150.324978.91528@grasshopper.cs.duke.edu>
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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)? > > > > > > <...> > > > > > > > This may be the same problem OpenBSD has fixed last year in the > > > > handling of the idle loop. From the kerneltrap posting: > > > > > > <....> > > > > > > > First commit message: > > > > http://marc.theaimsgroup.com/?l=openbsd-cvs&m=111692513727274&w=2 > > > > > > > > The MFC with all changes in one commit message: > > > > http://marc.theaimsgroup.com/?l=openbsd-cvs&m=111859519015510&w=2 > > > > > > The bug they fixes was missing interrupts by both calling APM's idle > > > routine, which may hlt, and hlt'ing in the idle loop itself. Since I > > > have no idea what acpi is doing, I got excited about this. > > > > > > Alas, it seems like this isn't it. I pointed cpu_idle_hook back to > > > cpu_idle_default and away from acpi_cpu_idle, but that made no > > > difference. > > > > 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. > Would you expect ULE to do better? I've noticed that if I screw up > the time state of the machine by switching between ACPI-fast and TSC > timecounters, performance for TCP ping-pongs goes all over the map... No ideas on this one. :( -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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