linux-kernel - Re: RFC: issues concerning the next NAPI interface

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Message-ID: <20070824165110.GH4282@austin.ibm.com>
Date:	Fri, 24 Aug 2007 11:51:10 -0500
From:	linas@...tin.ibm.com (Linas Vepstas)
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	Jan-Bernd Themann <ossthema@...ibm.com>,
	Thomas Klein <tklein@...ibm.com>, Marcus@...abs.org,
	Jan-Bernd Themann <themann@...ibm.com>,
	netdev <netdev@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Christoph Raisch <raisch@...ibm.com>,
	linux-ppc <linuxppc-dev@...abs.org>, akepner@....com,
	Eder <meder@...ibm.com>,
	Stefan Roscher <stefan.roscher@...ibm.com>
Subject: Re: RFC: issues concerning the next NAPI interface

On Fri, Aug 24, 2007 at 08:52:03AM -0700, Stephen Hemminger wrote:
> 
> You need hardware support for deferred interrupts. Most devices have it (e1000, sky2, tg3)
> and it interacts well with NAPI. It is not a generic thing you want done by the stack,
> you want the hardware to hold off interrupts until X packets or Y usecs have expired.

Just to be clear, in the previous email I posted on this thread, I
described a worst-case network ping-pong test case (send a packet, wait
for reply), and found out that a deffered interrupt scheme just damaged
the performance of the test case.  Since the folks who came up with the
test case were adamant, I turned off the defferred interrupts.  
While defferred interrupts are an "obvious" solution, I decided that 
they weren't a good solution. (And I have no other solution to offer).

--linas

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