Re: [PATCH 2/5] forcedeth: interrupt handling cleanup

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Yinghai Lu wrote:
On 10/7/07, Jeff Garzik <[email protected]> wrote:
Yinghai Lu wrote:
On 10/6/07, Jeff Garzik <[email protected]> wrote:
commit a606d2a111cdf948da5d69eb1de5526c5c2dafef
Author: Jeff Garzik <[email protected]>
Date:   Fri Oct 5 22:56:05 2007 -0400

    [netdrvr] forcedeth: interrupt handling cleanup

    * nv_nic_irq_optimized() and nv_nic_irq_other() were complete duplicates
      of nv_nic_irq(), with the exception of one function call.  Consolidate
      all three into a single interrupt handler, deleting a lot of redundant
      code.

    * greatly simplify irq handler locking.

      Prior to this change, the irq handler(s) would acquire and release
      np->lock for each action (RX, TX, other events).

      For the common case -- RX or TX work -- the lock is always acquired,
      making all successive acquire/release combinations largely redundant.

      Acquire the lock at the beginning of the irq handler, and release it at
      the end of the irq handler.  This is simple, easy, and obvious.

    * remove irq handler work loop.

      All interesting events emanating from the irq handler either have
      their own work loops, or they poke a timer into action.

      Therefore, delete the pointless master interrupt handler work loop.

    Signed-off-by: Jeff Garzik <[email protected]>

Do you have ideas/suggestions for a different method?

in the e1000 driver, it has seperate handler for msi and ioapic.

but in forcedeth, the nv_nic_irq_optimized keep check msi_flags...,
with num of msi interrupt number, that could cause cpu loading get a
little bit high..., even the network performance is ok.

With all the activity in the interrupt handler, a few in-cache branches are definitely going to be lost in the noise.

Separating the interrupt handlers between MSI and non-MSI tends to be of more benefit when the separation is accompanied by more efficient locking in the MSI interrupt handler, or a different mode of interrupt clear, or some other attribute.

Though CPU usage would be a good thing to measure, with these patches.

	Jeff




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