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Date: Tue, 24 Nov 2009 00:59:16 -0800 From: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Yong Zhang <yong.zhang0@...il.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "arjan@...ux.jf.intel.com" <arjan@...ux.jf.intel.com>, "davem@...emloft.net" <davem@...emloft.net>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH] irq: Add node_affinity CPU masks for smarter irqbalance hints On Tue, 2009-11-24 at 01:38 -0700, Peter Zijlstra wrote: > On Mon, 2009-11-23 at 15:32 -0800, Waskiewicz Jr, Peter P wrote: > > > Unfortunately, a driver can't. The irq_set_affinity() function isn't > > exported. I proposed a patch on netdev to export it, and then to tie down > > an interrupt using IRQF_NOBALANCING, so irqbalance won't touch it. That > > was rejected, since the driver is enforcing policy of the interrupt > > balancing, not irqbalance. > > Why would a patch touching the irq subsystem go to netdev? The only change to the IRQ subsystem was: EXPORT_SYMBOL(irq_set_affinity); The majority of the changeset was for the ixgbe driver. > What is wrong with exporting irq_set_affinity(), and wtf do you need > IRQF_NOBALANCING for? > Again, the pushback I received was with allowing anything other than irqbalance to dictate interrupt affinity policy. And if I set interrupt affinity from the driver or from /proc, irqbalance will happily rebalance the interrupt elsewhere. The IRQF_NOBALANCING flag will prevent irqbalance from being able to move the interrupt. > > I and Jesse Brandeburg had a meeting with Arjan about this. What we came > > up with was this interface, so drivers can set what they'd like to see, if > > irqbalance decides to honor it. That way interrupt affinity policies are > > set only by irqbalance, but this interface gives us a mechanism to hint to > > irqbalance what we'd like it to do. > > If all you want is to expose policy to userspace then you don't need any > of this, simply expose the NICs home node through a sysfs device thingy > (I was under the impression its already there somewhere, but I can't > ever find anything in /sys). > > No need what so ever to poke at the IRQ subsystem. The point is we need something common that the kernel side (whether a driver or /proc can modify) that irqbalance can use. > > Also, if you use the /proc interface to change smp_affinity on an > > interrupt without any of these changes, irqbalance will override it on its > > next poll interval. This also is not desirable. > > This all sounds backwards.. we've got a perfectly functional interface > for affinity -- which people object to being used for some reason. So > you add another interface on top, and that is ok? > But it's not functional. If I set the affinity in smp_affinity, then irqbalance will override it 10 seconds later. > All the while not CC'ing the IRQ folks,.. brilliant approach. If I knew who I should CC, I'd be happy to add them. Can you provide email addresses please? Cheers, -PJ Waskiewicz -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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