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Message-ID: <20070913204443.GB5386@csclub.uwaterloo.ca>
Date: Thu, 13 Sep 2007 16:44:43 -0400
From: lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To: Venkat Subbiah <venkats@...nite.com>
Cc: Chris Snook <csnook@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: irq load balancing
On Thu, Sep 13, 2007 at 01:31:39PM -0700, Venkat Subbiah wrote:
> Doing it in a round-robin fashion will be disastrous for performance.
> Your cache miss rate will go through the roof and you'll hit the slow
> paths in the network stack most of the time.
> > Most of the work in my system is spent in enrypt/decrypting traffic.
> Right now all this is done in a tasklet within the softirqd and hence
> all landing up on the same CPU.
> On the receive side it'a packet handler that handles the traffic. On the
> tx side it's done within the transmit path of the packet. So would
> re-architecting this to move the rx packet handler to a different kernel
> thread(with smp affinity to one CPU) and tx to a different kernel
> thread(with SMP affinity to a different CPU) be advisable.
> What's the impact on cache miss and slowpath/fastpath in network stack.
Since most network devices have a single status register for both
receiver and transmit (and errors and the like), which needs a lock to
protect access, you will likely end up with serious thrashing of moving
the lock between cpus.
--
Len Sorensen
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