netdev - Re: [Lsf] [LSF/MM TOPIC] Generic page-pool recycle facility?

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Date:	Thu, 7 Apr 2016 22:38:53 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	"Waskiewicz, PJ" <PJ.Waskiewicz@...app.com>
Cc:	"lsf@...ts.linux-foundation.org" <lsf@...ts.linux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"bblanco@...mgrid.com" <bblanco@...mgrid.com>,
	"alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
	"James.Bottomley@...senPartnership.com" 
	<James.Bottomley@...senPartnership.com>,
	"tom@...bertland.com" <tom@...bertland.com>,
	"lsf-pc@...ts.linux-foundation.org" 
	<lsf-pc@...ts.linux-foundation.org>, brouer@...hat.com
Subject: Re: [Lsf] [LSF/MM TOPIC] Generic page-pool recycle facility?

On Thu, 7 Apr 2016 19:48:50 +0000
"Waskiewicz, PJ" <PJ.Waskiewicz@...app.com> wrote:

> On Thu, 2016-04-07 at 16:17 +0200, Jesper Dangaard Brouer wrote:
> > (Topic proposal for MM-summit)
> > 
> > Network Interface Cards (NIC) drivers, and increasing speeds stress
> > the page-allocator (and DMA APIs).  A number of driver specific
> > open-coded approaches exists that work-around these bottlenecks in
> > the
> > page allocator and DMA APIs. E.g. open-coded recycle mechanisms, and
> > allocating larger pages and handing-out page "fragments".
> > 
> > I'm proposing a generic page-pool recycle facility, that can cover
> > the
> > driver use-cases, increase performance and open up for zero-copy RX.  
> 
> Is this based on the page recycle stuff from ixgbe that used to be in
> the driver?  If so I'd really like to be part of the discussion.

Okay, so it is not part of the driver any-longer?  I've studied the
current ixgbe driver (and other NIC drivers) closely.  Do you have some
code pointers, to this older code?

The likely-fastest recycle code I've see is in the bnx2x driver.  If
you are interested see: bnx2x_reuse_rx_data().  Again is it a bit
open-coded produce/consumer ring queue (which would be nice to also
cleanup).

To amortize the cost of allocating a single page, most other drivers
use the trick of allocating a larger (compound) page, and partition
this page into smaller "fragments".  Which also amortize the cost of
dma_map/unmap (important on non-x86).

This is actually problematic performance wise, because packet-data
(in these page fragments) only get DMA_sync'ed, and is thus considered
"read-only".  As netstack need to write packet headers, yet-another
(writable) memory area is allocated per packet (plus the SKB meta-data
struct).

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer