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SubjectRe: [PATCH] Re: Bad network performance over 2Gbps
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By default also without IRQBALANCE enabled in kernel, APIC or someone else distributing interrupts over processors too.
There is no irqbalance daemon or whatever.

For example:
Router-KARAM ~ # cat /proc/interrupts
CPU0 CPU1
0: 87956938 1403052485 IO-APIC-edge timer
1: 0 2 IO-APIC-edge i8042
9: 0 0 IO-APIC-fasteoi acpi
19: 140 5714 IO-APIC-fasteoi ohci_hcd:usb1, ohci_hcd:usb2
24: 675673280 1186506694 IO-APIC-fasteoi eth2
26: 717865662 2201633562 IO-APIC-fasteoi eth0
27: 1869190 23075556 IO-APIC-fasteoi eth1
NMI: 0 0 Non-maskable interrupts
LOC: 1403052485 87956683 Local timer interrupts
RES: 75059 25408 Rescheduling interrupts
CAL: 99542 83 function call interrupts
TLB: 616 200 TLB shootdowns
TRM: 0 0 Thermal event interrupts
SPU: 0 0 Spurious interrupts
ERR: 0
MIS: 0

sunfire-1 ~ # cat config|grep -i irq
CONFIG_GENERIC_HARDIRQS=y
CONFIG_GENERIC_IRQ_PROBE=y
CONFIG_GENERIC_PENDING_IRQ=y
# CONFIG_IRQBALANCE is not set
CONFIG_HT_IRQ=y
# CONFIG_HPET_RTC_IRQ is not set
CONFIG_TRACE_IRQFLAGS_SUPPORT=y
# CONFIG_DEBUG_SHIRQ is not set

Is it harmful too?

On Thursday 17 April 2008 20:37, Kok, Auke wrote:
> Anton Titov wrote:
> > On Tue, 2008-04-15 at 16:59 -0400, Chris Snook wrote:
> >> Still, I think you're on to something here. Disabling NAPI and instead
> >> tuning the cards' interrupt coalescing settings might allow irqbalance
> >> to do a better job than it is currently.
> >
> > Disabling NAPI allowed me to push as much as 3.5Gbit out of the same
> > server with ~ 20% of time CPUs doing software interrupts.
>
> yes, I really don't see this is such an amazing discovery - the in-kernel
> irqbalance code is totally wrong for network interrupts (and probably for most
> interrupts).
>
> on your system with 6 network interrupts it blows chunks and it's not NAPI that is
> the issue - NAPI will work just fine on it's own. By disabling NAPI and reverting
> to the in-driver irq moderation code you've effectively put the in-kernel
> irqbalance code to the sideline and this is what makes it work again.
>
> It's not the right solution.
>
> We keep seing this exact issue pop up everywhere - especially with e1000(e)
> datacenter users - this code _has_ to go or be fixed. Since there is a perfectly
> viable solution, I strongly suggest disabling it.
>
> This is not the first time I've sent this patch out in some form...
>
> Auke
>
>
> ---
> [X86] IRQBALANCE: Mark as BROKEN and disable by default
>
> The IRQBALANCE option causes interrupts to bounce all around on SMP systems
> quickly burying the CPU in migration cost and cache misses. Mainly affected are
> network interrupts and this results in one CPU pegged in softirqd completely.
>
> Disable this option and provide documentation to a better solution (userspace
> irqbalance daemon does overall the best job to begin with and only manual setting
> of smp_affinity will beat it).
>
> Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
>
> ---
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 6c70fed..956aa22 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1026,13 +1026,17 @@ config EFI
> platforms.
>
> config IRQBALANCE
> - def_bool y
> + def_bool n
> prompt "Enable kernel irq balancing"
> - depends on X86_32 && SMP && X86_IO_APIC
> + depends on X86_32 && SMP && X86_IO_APIC && BROKEN
> help
> The default yes will allow the kernel to do irq load balancing.
> Saying no will keep the kernel from doing irq load balancing.
>
> + This option is known to cause performance issues on SMP
> + systems. The preferred method is to use the userspace
> + 'irqbalance' daemon instead. See http://irqbalance.org/.
> +
> config SECCOMP
> def_bool y
> prompt "Enable seccomp to safely compute untrusted bytecode"
> --
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>

--
------
Technical Manager
Virtual ISP S.A.L.
Lebanon


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