netdev - Re: [PATCH 2/3] net: Add net device irq siloing feature

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Message-ID: <367764507.40661.1302929544356.JavaMail.root@tahiti.vyatta.com>
Date:	Fri, 15 Apr 2011 21:52:24 -0700 (PDT)
From:	Stephen Hemminger <stephen.hemminger@...tta.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	Dimitris Michailidis <dm@...lsio.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Tom Herbert <therbert@...gle.com>,
	Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: [PATCH 2/3] net: Add net device irq siloing feature


> On Fri, Apr 15, 2011 at 11:49:03PM +0100, Ben Hutchings wrote:
> > On Fri, 2011-04-15 at 16:17 -0400, Neil Horman wrote:
> > > Using the irq affinity infrastrucuture, we can now allow net
> > > devices to call
> > > request_irq using a new wrapper function (request_net_irq), which
> > > will attach a
> > > common affinty_update handler to each requested irq. This affinty
> > > update mechanism correlates each tracked irq to the flow(s) that
> > > said irq processes
> > > most frequently. The highest traffic flow is noted, marked and
> > > exported to user
> > > space via the affinity_hint proc file for each irq. In this way,
> > > utilities like
> > > irqbalance are able to determine which cpu is recieving the most
> > > data from each
> > > rx queue on a given NIC, and set irq affinity accordingly.
> > [...]
> >
> > Is irqbalance expected to poll the affinity hints? How often?
> >
> Yes, its done just that for quite some time. Intel added that ability
> at the
> same time they added the affinity_hint proc file. Irqbalance polls the
> affinity_hint file at the same time it rebalances all irqs (every 10
> seconds). If the affinity_hint is non-zero, irqbalance just copies it
> to smp_affinity for
> the same irq. Up until now thats been just about dead code because
> only ixgbe
> sets affinity_hint. Thats why I added the affinity_alg file, so
> irqbalance could do something more intellegent than just a blind copy.
> With the patch that
> I referenced I added code to irqbalance to allow it to preform
> different balancing methods based on the output of affinity_alg.
> Neil

I hate the way more and more interfaces are becoming device driver
specific. It makes it impossible to build sane management infrastructure
and causes lots of customer and service complaints.

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