netdev - Re: [PATCH net-next v6 05/12] net: homa: create homa_rpc.h and homa

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Message-ID: <CANn89iJmbefLpPW-jgJjFkx79yso3jUUzuH0voPaF+2Kz3EW2g@mail.gmail.com>
Date: Wed, 29 Jan 2025 18:04:36 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: John Ousterhout <ouster@...stanford.edu>
Cc: Paolo Abeni <pabeni@...hat.com>, Netdev <netdev@...r.kernel.org>, 
	Simon Horman <horms@...nel.org>, Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next v6 05/12] net: homa: create homa_rpc.h and homa_rpc.c

On Wed, Jan 29, 2025 at 5:55 PM John Ousterhout <ouster@...stanford.edu> wrote:
>
> On Wed, Jan 29, 2025 at 8:50 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Wed, Jan 29, 2025 at 5:44 PM John Ousterhout <ouster@...stanford.edu> wrote:
> > >
> > > GRO is implemented in the "full" Homa (and essential for decent
> > > performance); I left it out of this initial patch series to reduce the
> > > size of the patch. But that doesn't affect the cost of freeing skbs.
> > > GRO aggregates skb's into batches for more efficient processing, but
> > > the same number of skb's ends up being freed in the end.
> >
> > Not at all, unless GRO is forced to use shinfo->frag_list.
> >
> > GRO fast path cooks a single skb for a large payload, usually adding
> > as many page fragments as possible.
>
> Are you referring to hardware GRO or software GRO? I was referring to
> software GRO, which is what Homa currently implements. With software
> GRO there is a stream of skb's coming up from the driver; regardless
> of how GRO re-arranges them, each skb eventually has to be freed, no?

I am referring to software GRO.
We do not allocate/free skbs for each aggregated segment.
napi_get_frags() & napi_reuse_skb() for details.