Re: e1000 driver 2.6.18 - how to waste processor cycles

[Jeff V. Merkey]

Jeff V. Merkey wrote:

> Jesse Brandeburg wrote:
>
> > On 11/9/06, Jeffrey V. Merkey <jmerkey@xxxxxxxxxxxxxxxxxx> wrote:
> >
> > > In the case I am referring to, the memory is already mapped with a
> > > previous call, which means it may be getting
> > > mapped twice.
> >
> >
> >
> > I guess maybe I'm not keeping up with you.  This is what I see looking
> > in 2.6.18, i see e1000_clean_rx_irq:
>
>
>
> Check e1000_alloc_rx_buffers:
>
> if (skb already exists in ring buffer)
>  goto map_skb:
> else
>   dev_alloc_skb
>  ( drop through to map_skb)
>
>
> map_skb:
>  pci_map_single
>
> Jeff


> > check done bit
> > pci_unmap_single
> > copybreak and recycle
> > OR
> > hand buffer up stack
> >
> > the only branch before the unmap is the napi break out, and in that
> > case we don't change any memory state, so alloc will not do anything.
> >
> > As for alloc rx, we always map, because we always unmapped.
Unmapping every single buffer in rx_irq the remapping them in 
alloc_rx_buffers is wasteful of cycles. 

Jeff

> > Did I miss something?  I would appreciate a more detailed explanation
> > of what you see going wrong.
>
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