netdev - Re: How do I know my driver support RSS?

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Message-ID: <1330899837.3022.17.camel@deadeye>
Date:	Sun, 4 Mar 2012 22:23:57 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Yuehai Xu <yuehaixu@...il.com>
CC:	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>, <yhxu@...ne.edu>,
	<sbw@....edu>
Subject: Re: How do I know my driver support RSS?

On Sat, 2012-03-03 at 23:30 -0500, Yuehai Xu wrote:
> On Sat, Mar 3, 2012 at 7:10 PM, Ben Hutchings <bhutchings@...arflare.com> wrote:
> > On Sat, 2012-03-03 at 16:25 -0500, Yuehai Xu wrote:
> > [...]
> >> Since I read the following statements from a paper, "we use a separate
> >> hardware receive and transmit queue for each core and configure the
> >> IXGBE to inspect the port number in each incoming packet header, place
> >> the packet on the queue dedicated to the associated memcached's core,
> >> and deliver the receive interrupt to that core." and the background of
> >> this configuration is that each memcached is pinned to a separate core
> >> and has its own UDP port. It seems that IXGBE's driver can detect UDP
> >> packets according to their port numbers and put these packets into
> >> corresponding receive queues in the hardware, is this achieved by
> >> configuring RSS in IXGBE? If it is, I am wondering whether bnx2
> >> supports RSS and whether it can configure in the same way.
> >>
> >> I appreciate any help for this.
> >
> > You're confusing RSS (flow hashing) with flow steering.  These are both
> > explained in Documentation/network/scaling.txt.
> >
> > Ben.
> >
> I appreciate your replying!! What confuses me is that for each UDP
> socket with exclusive port number, it has RX queue in transport layer,
> and network card might also have multiple RX queues. These two queues
> are definitely different. So, is it possible to configure network card
> to put packets to queues(RX queues in network card) according to hash?

Yes.

> I read the codes of RPS/RFS, it seems that packets are put into queues
> in transport layer of sockets instead of queues in network card. Am I
> correct?
>
> I appreciate any replies.

No, that's not right.  There are also per-CPU queues of packets to be
processed.  So a packet can go from the port into a hardware RX queue,
then to a per-CPU queue for protocol processing on that CPU, then to a
per-socket queue.  By default, the protocol processing for a packet will
be done on the same CPU that took it off the hardware queue, but RPS and
RFS can transfer packets to other per-CPU queues.  It is possible to
improve on this with the hardware flow steering mechanisms discussed in
that document.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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