Re: Info: NAPI performance at "low" loads

[Jeff Garzik <jgarzik@xxxxxxxxxxxxxxxx>]

David S. Miller wrote:
>    From: Jeff Garzik <jgarzik@xxxxxxxxxxxxxxxx>
>    Date: Tue, 17 Sep 2002 17:54:42 -0400
>
>    David S. Miller wrote:
>    > Any driver should be able to get the NAPI overhead to max out at
>    > 2 PIOs per packet.
>    
>    Just to pick nits... my example went from 2 or 3 IOs [depending on the 
>    presence/absence of a work loop] to 6 IOs.
>    
> I mean "2 extra PIOs" not "2 total PIOs".
> I think it's doable for just about every driver, even tg3 with it's
> weird semaphore scheme takes 2 extra PIOs worst case with NAPI.
>
> The semaphore I have to ACK anyways at hw IRQ time anyways, and since
> I keep a software copy of the IRQ masking register, mask and unmask
> are each one PIO.

You're looking at at least one extra get-irq-status too, at least in the 
classical 10/100 drivers I'm used to seeing...
        Jeff