Re: [Intel-wired-lan] [PATCH net v2] igb: cope with large MAX_SKB_FRAGS

[Corinna Vinschen]

Hi Eric,

sorry for the very late reply, I was offline for quite some time
and then other things took over.

On Apr 26 19:54, Eric Dumazet wrote:
> On Fri, Apr 26, 2024 at 4:30 PM Corinna Vinschen <vinschen@xxxxxxxxxx> wrote:
> >
> > Hi Eric,
> >
> > On Apr 23 16:10, Eric Dumazet wrote:
> > > On Tue, Apr 23, 2024 at 3:47 PM Corinna Vinschen <vinschen@xxxxxxxxxx> wrote:
> > > >
> > > > From: Paolo Abeni <pabeni@xxxxxxxxxx>
> > > >
> > > > Sabrina reports that the igb driver does not cope well with large
> > > > MAX_SKB_FRAG values: setting MAX_SKB_FRAG to 45 causes payload
> > > > corruption on TX.
> > > >
> > > > An easy reproducer is to run ssh to connect to the machine.  With
> > > > MAX_SKB_FRAGS=17 it works, with MAX_SKB_FRAGS=45 it fails.
> > > > [...]
> > > > @@ -4833,6 +4833,7 @@ static void igb_set_rx_buffer_len(struct igb_adapter *adapter,
> > > >
> > > >  #if (PAGE_SIZE < 8192)
> > > >         if (adapter->max_frame_size > IGB_MAX_FRAME_BUILD_SKB ||
> > > > +           SKB_HEAD_ALIGN(adapter->max_frame_size) > (PAGE_SIZE / 2) ||
> > >
> > > I wonder if adding IGB_SKB_PAD would be needed ?
> > >
> > > adapter->max_frame_size does not seem to include it.
> > >
> > > I would try using all mtus between 1200 and 1280 to make sure this works.
> >
> > Erm... did you mean between 1500 and 1580 by any chance?  1200 doesn't
> > really seem to make sense...
> 
> No, I meant 1200 to 1280 .  IPv4 should accept these MTU .
> 
> 1200 + 768 = 1968
> 1280 + 768 = 2048 (2 KB)
> 
> I am worried of some padding that would cross 2048 bytes boundary,
> while SKB_HEAD_ALIGN(adapter->max_frame_size) could still be < 2048
> 
> 
> >
> > I tested this patch now with mtu 1500, 1540 and 1580 successfully.
> >
> > Either way, I'm just heading into vacation, so I guess I'll pick this up
> > again when I'm back, unless Paolo takes another look during my absence.
> >
> 
> I guess your patch is better than nothing, this can be refined if
> necessary later.

I now tested the patch with all MTUs between 1200 and 1280 and it
works as desired.  I just sent a v3.


Thanks,
Corinna