netdev - Re: [PATCH 1/2]: softirq: Add support for triggering softirq work on softirqs.

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Date:	Fri, 19 Sep 2008 13:29:51 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	stephen.hemminger@...tta.com
Cc:	jens.axboe@...cle.com, netdev@...r.kernel.org,
	nickpiggin@...oo.com.au, ilpo.jarvinen@...sinki.fi
Subject: Re: [PATCH 1/2]: softirq: Add support for triggering softirq work
 on softirqs.

From: Stephen Hemminger <stephen.hemminger@...tta.com>
Date: Fri, 19 Sep 2008 09:57:30 -0700 (PDT)

> I wonder if the added overhead of local_irq_disable/local_irq_enable is
> killing any performance gain. Certainly it adds more latency to a sensitive code path.
> 
> Is there a good lock-less solution?

The cross-cpu IPI is 1,000 times more expensive than the local IRQ
enable/disable (on x86 it's a bunch of APIC programming), so if you're
looking for cost analysis start there.
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