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

[Stephen Hemminger <shemminger@vyatta.com>]

On Wed, 15 Dec 2010 17:14:25 -0800
Fenghua Yu <fenghua.yu@intel.com> wrote:

> 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 <fenghua.yu@intel.com>
> > > 
> > > 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.

Do we really want to expose this kind of internals to userspace?
The problem is once exposed, it becomes a kernel ABI and can not ever
change. 
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