netdev - Re: [PATCH v2 46/46] net: mark drivers that drop packets from rx queue head under memory pressure

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Date:	Mon, 11 Jul 2011 12:04:47 +0200
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Eilon Greenstein <eilong@...adcom.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Hartley Sweeten <hsweeten@...ionengravers.com>,
	Michael Chan <mchan@...adcom.com>,
	Guo-Fu Tseng <cooldavid@...ldavid.org>,
	Realtek linux nic maintainers <nic_swsd@...ltek.com>,
	Francois Romieu <romieu@...zoreil.com>,
	Stephen Hemminger <shemminger@...ux-foundation.org>,
	Matthew Carlson <mcarlson@...adcom.com>,
	Jon Mason <jdmason@...zu.us>
Subject: Re: [PATCH v2 46/46] net: mark drivers that drop packets from rx
 queue head under memory pressure

On Mon, Jul 11, 2011 at 09:47:08AM +0300, Eilon Greenstein wrote:
> On Sun, 2011-07-10 at 17:52 -0700, Michał Mirosław wrote:
> > Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> > ---
> 
> > diff --git a/drivers/net/bnx2x/bnx2x_cmn.c b/drivers/net/bnx2x/bnx2x_cmn.c
> > index 4f9164c..a6da01a 100644
> > --- a/drivers/net/bnx2x/bnx2x_cmn.c
> > +++ b/drivers/net/bnx2x/bnx2x_cmn.c
> > @@ -673,6 +673,9 @@ int bnx2x_rx_int(struct bnx2x_fastpath *fp, int budget)
> >  				goto reuse_rx;
> >  			}
> >  
> > +#warning drops packets from rx queue head on memory pressure
> > +#warning (like dev_skb_finish_rx_dma_refill() users)
> > +
> 
> We have the dropless_fc module parameter that can be configured if the
> user prefers pausing on host memory pressure - the problem with that
> feature is that it is enough that one of the ring runs out of memory and
> the entire port is stopped. When running with 16 rings, this can lead to
> serious throughput degradation - this is why it is kept as a user
> configurable option.

>From the code it look like dropless_fc just enables sending of pause
frames.  If that's disabled, then what happens when one queue runs out
of free rx buffers?

Best Regards,
Michał Mirosław
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