netdev - Re: [PATCH] Multiqueue macvtap driver

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Message-ID: <OF8519C301.F0E5FA07-ON65257772.004983CC-65257773.00453C8B@in.ibm.com>
Date:	Mon, 2 Aug 2010 18:07:40 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	arnd@...db.de, bhutchings@...arflare.com, mst@...hat.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH] Multiqueue macvtap driver

Thanks Ben & Dave. A question though - which of the following
is preferable for the macvtap driver:

1. Calculate flow and use that to find a queue; or
2. First check if skb_rx_queue_recorded is true and if so use
    that; otherwise calculate the flow as in #1.

I guess #1 is better, since packets for a single flow will go to the
same queue even if they arrive on different rxqs of a mq driver.
But I want to make sure.

Thanks,

- KK

David Miller <davem@...emloft.net> wrote on 08/01/2010 01:04:06 PM:

> David Miller <davem@...emloft.net>
> 08/01/2010 01:04 PM
>
> To
>
> bhutchings@...arflare.com
>
> cc
>
> Krishna Kumar2/India/IBM@...IN, arnd@...db.de,
> netdev@...r.kernel.org, mst@...hat.com
>
> Subject
>
> Re: [PATCH] Multiqueue macvtap driver
>
> From: Ben Hutchings <bhutchings@...arflare.com>
> Date: Sat, 31 Jul 2010 20:18:27 +0100
>
> > On Sat, 2010-07-31 at 19:27 +0530, Krishna Kumar wrote:
> > [...]
> >> @@ -136,39 +158,68 @@ static void macvtap_put_queue(struct mac
> >>  }
> >>
> >>  /*
> >> - * Since we only support one queue, just dereference the pointer.
> >> + * Select a queue based on the rxq of the device on which this packet
> >> + * arrived. If the incoming device is not mq, then use our cpu number
> >> + * to select a queue. vlan->numvtaps is cached in case it changes
> >> + * during the execution of this function.
> >>   */
> > [...]
> >
> > This can result in reordering if a single-queue device's RX interrupt's
> > CPU affinity is changed.  We generally try to avoid that.  You should
> > really use or generate a flow hash.  There is code for this in
> > net/core/dev.c:get_rps_cpu() which could be factored out into a
separate
> > function.
>
> Agreed.

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