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

[Jeff Garzik]

Yinghai Lu wrote:
> On 10/7/07, Jeff Garzik <jeff@xxxxxxxxxx> wrote:
> > Yinghai Lu wrote:
> > > On 10/6/07, Jeff Garzik <jeff@xxxxxxxxxx> wrote:
> > > > commit a606d2a111cdf948da5d69eb1de5526c5c2dafef
> > > > Author: Jeff Garzik <jeff@xxxxxxxxxx>
> > > > 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 <jgarzik@xxxxxxxxxx>
> > 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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