netdev - Re: [PATCH v4 1/1] rps: core implementation

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Message-Id: <20091120.160507.110482370.davem@davemloft.net>
Date:	Fri, 20 Nov 2009 16:05:07 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	therbert@...gle.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH v4 1/1] rps: core implementation

From: Tom Herbert <therbert@...gle.com>
Date: Fri, 20 Nov 2009 15:50:03 -0800

> We only set the bit in remote_softirq_cpus in here.  The actual IPIs
> are sent at the end net_rx_action.  I'm not exactly sure what you're
> thinking on this...

You're scheduling a softirq so you can schedule remote softirqs.

Just do that "for each rps cpu" loop at the end of NAPI ->poll()
processing.  In fact that seems to be what you're doing :-)

I guess my confusion is from the:

				__raise_softirq_irqoff(NET_RX_SOFTIRQ);

you are doing as you set the cpus in rps_remote_softirq_cpus.

Why do you need to schedule the local RX softirq, when we know we're
in a NAPI poll loop and thus that we're in a softirq, and thus that we
will fire off the IPIs at the end of net_rx_action()?

That's what you're doing, the softirq raising just seems superfluous.
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