lkml.org 
[lkml]   [2010]   [Dec]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/3] Kernel interfaces for multiqueue aware socket
From
Date
Le mercredi 15 décembre 2010 à 17:14 -0800, Fenghua Yu a écrit :
> 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)
> >

No data for this NUMA problem ?
We had to convince Andrew Morton for this patch to get in.

> > > 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.
>

Yes, we also should address other sockets, with generic mechanisms.

> > 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.
>

We really need to be smarter than that, not adding raw API.

Tom Herbert added RPS, RFS, XPS, in a way applications dont have to use
special API, just run normal code.

Please understand that using 8 AF_PACKET sockets bound to a given device
is a total waste, because the way we loop on ptype_all before entering
AF_PACKET code, and in 12% of the cases deliver the packet into a queue,
and 77.5% of the case reject the packet.

This is absolutely not scalable to say... 64 queues.

I do believe we can handle that using one AF_PACKET socket for the RX
side, in order to not slow down the loop we have in
__netif_receive_skb()

list_for_each_entry_rcu(ptype, &ptype_all, list) {
...
deliver_skb(skb, pt_prev, orig_dev);
}

(Same problem with dev_queue_xmit_nit() by the way, even worse since we
skb_clone() packet _before_ entering af_packet code)

And we can change af_packet to split the load to N skb queues or N ring
buffers, N not being necessarly number of NIC queues, but the number
needed to handle the expected load.

There is nothing preventing us changing af_packet/udp/tcp_listener to
something more scalable in itself, using a set of receive queues, and
NUMA friendly data set. We did multiqueue for a net_device like this,
not adding N pseudo devices as we could have done.



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2010-12-16 05:47    [W:0.120 / U:0.432 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site