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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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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