Subject: Re: [PATCH 1/3] Kernel interfaces for multiqueue aware socket

From: Fenghua Yu <[email-masked]>
Date: Wed, 15 Dec 2010 17:14:25 -0800

On Wed, Dec 15, 2010 at 12:48:38PM -0800, Eric Dumazet wrote:
> Le mercredi 15 décembre 2010 à 12:02 -0800, Fenghua Yu a écrit :
> > From: Fenghua Yu <[email-masked]>
> > 
> > Multiqueue and multicore provide packet parallel processing methodology.
> > Current kernel and network drivers place one queue on one core. But the higher
> > level socket doesn't know multiqueue. Current socket only can receive or send
> > packets through one network interfaces. In some cases e.g. multi bpf filter
> > tcpdump and snort, a lot of contentions come from socket operations like ring
> > buffer. Even if the application itself has been fully parallelized and run on
> > multi-core systems and NIC handlex tx/rx in multiqueue in parallel, network layer
> > and NIC device driver assemble packets to a single, serialized queue. Thus the
> > application cannot actually run in parallel in high speed.
> > 
> > To break the serialized packets assembling bottleneck in kernel, one way is to
> > allow socket to know multiqueue associated with a NIC interface. So each socket
> > can handle tx/rx in one queue in parallel.
> > 
> > Kernel provides several interfaces by which sockets can be bound to rx/tx queues.
> > User applications can configure socket by providing several sockets that each
> > bound to a single queue, applications can get data from kernel in parallel. After
> > that, competitions mentioned above can be removed.
> > 
> > With this patch, the user-space receiving speed on a Intel SR1690 server with
> > a single L5640 6-core processor and a single ixgbe-based NIC goes from 0.73Mpps
> > to 4.20Mpps, nearly a linear speedup. A Intel SR1625 server two E5530 4-core
> > processors and a single ixgbe-based NIC goes from 0.80Mpps to 4.6Mpps. We noticed
> > the performance penalty comes from NUMA memory allocation.
> > 
> 
> ??? please elaborate on these NUMA memory allocations. This should be OK
> after commit 564824b0c52c34692d (net: allocate skbs on local node)
> 
> > This patch set provides kernel ioctl interfaces for user space. User space can
> > either directly call the interfaces or libpcap interfaces can be further provided
> > on the top of the kernel ioctl interfaces.
> 
> So, say we have 8 queues, you want libpcap opens 8 sockets, and bind
> them to each queue. Add a bpf filter to each one of them. This seems not
> generic way, because it wont work for an UDP socket for example.

This only works for AF_PACKET like this patch set shows.

> And you already can do this using SKF_AD_QUEUE (added in commit
> d19742fb)

SKF_AD_QUEUE doesn't know number of rx queues. Thus user application can't
specify right SKF_AD_QUEUE.

SKF_AD_QUEUE only works for rx. There is no queue bound interfaces for tx.

I can change the patch set to use SKF_AD_QUEUE by removing the set rx queue
interface and still keep interfaces of
#define SIOGNUMRXQUEUE 0x8939  /* Get number of rx queues. */
#define SIOGNUMTXQUEUE 0x893A  /* Get number of tx queues. */
#define SIOSTXQUEUEMAPPING     0x893C  /* Set tx queue mapping. */
#define SIOGRXQUEUEMAPPING     0x893D  /* Get rx queue mapping. */
#define SIOGTXQUEUEMAPPING     0x893E  /* Get tx queue mapping. */

> 
> Also your AF_PACKET patch only address mmaped sockets.
> 
The new patch set will use SKF_AD_QUEUE for rx. So it won't be limited to mmaped
sockets.