Date: Sat, 04 Feb 2006 07:58:37 +0800 From: David Xu <davidxu@freebsd.org> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: freebsd-current@freebsd.org Subject: Re: machdep.cpu_idle_hlt and SMP perf? Message-ID: <43E3EE2D.10001@freebsd.org> In-Reply-To: <17379.56708.421007.613310@grasshopper.cs.duke.edu> References: <17379.56708.421007.613310@grasshopper.cs.duke.edu>
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Andrew Gallatin wrote: >Why dooes machdep.cpu_idle_hlt=1 drop my 10GbE network rx >performance by a considerable amount (7.5Gbs -> 5.5Gbs)? > >I've (blindly) tried leaving machdep.cpu_idle_hlt=1 enabled >and playing with the vast array of kern.sched.ipiwakeup.* sysctls, >but receive performance remains limited to ~5.5Gb/sec or less. > >This is an 'AMD Athlon(tm) 64 X2 Dual Core Processor 3800+' running >FreeBSD-current as of about one week ago. The interrupt load is >about 22,000 device interrupts/sec (ithreaded). Interestingly, >the more I decrease the interrupt load by increasing the interrupt >coalescing timer, the worse the machdep.cpu_idle_hlt=1 case does. > >Is this just a case of the wakeup IPI taking a long time or blocking >on some lock? > >Drew > >PS: Here is what I mean: > > I am thinking if we can rewrite cpu idle code by using mwait instruction on pentium4, it should reduce latency, I don't know if Athlon 64 supports this instruction yet. David Xu
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