netdev - Re: Low performance Intel 10GE NIC (3.2.10) on 2.6.38 Kernel

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Date:	Thu, 07 Apr 2011 18:03:38 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	Wei Gu <wei.gu@...csson.com>, netdev <netdev@...r.kernel.org>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
Subject: Re: Low performance Intel 10GE NIC (3.2.10) on 2.6.38 Kernel

Le jeudi 07 avril 2011 à 08:58 -0700, Alexander Duyck a écrit :
> On 4/7/2011 4:46 AM, Eric Dumazet wrote:
> > Le jeudi 07 avril 2011 à 19:15 +0800, Wei Gu a écrit :
> >> Hi,
> >> I compile the ixgbe driver into the kernel and run the test again and also change the copy to clone in the fw hook
> >> This is the perf report while I was forwarding 150Kpps with
> >> The attached file include the basic info about my test system. Please let me know if I did some thing wrong.
> >>
> >> +     71.91%          swapper  [kernel.kallsyms]            [k] poll_idle
> >> +     10.43%          swapper  [kernel.kallsyms]            [k] intel_idle
> >> -      8.00%     ksoftirqd/24  [kernel.kallsyms]            [k] _raw_spin_unlock_irqrestore
> >> \u2592   - _raw_spin_unlock_irqrestore
> >> \u2592      - 42.25% alloc_iova
> >> \u2592           intel_alloc_iova
> >> \u2592           __intel_map_single
> >> \u2592           intel_map_page
> 
> I'm almost certain this is the issue here.  I am pretty sure the 
> intel_map_page call indicates that you are running with the Intel IOMMU 
> enabled.  As Eric suggested you can either rebuild your kernel with 
> "CONFIG_DMAR=N", or pass the kernel the parameter "intel_iommu=off" in 
> order to disable it so that it will instead just use SWIOTLB.

What's the purpose of intel_iommu ?

Could this be speedup if ixgbe uses a perqueue iommu context instead of
a per device, so that we dont hit a single spinlock ?


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