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Date: Wed, 29 Dec 2010 10:47:40 +0200 From: Pasi Kärkkäinen <pasik@....fi> To: "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com> Cc: Alkis Georgopoulos <alkisg@...il.com>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> Subject: Re: Bypass flow control problems On Tue, Dec 28, 2010 at 09:05:42PM -0800, Kirsher, Jeffrey T wrote: > On Dec 27, 2010, at 8:43, Pasi Kärkkäinen <pasik@....fi> wrote: > > > On Wed, Dec 22, 2010 at 07:51:31PM +0200, Alkis Georgopoulos wrote: > >> Hi, > >> > >> I'm an IT teacher/LTSP developer. In LTSP, thin clients are netbooted > >> from a server and receive a lot of X and remote disk traffic from it. > >> > >> Many installations have a gigabit NIC on the server, an unmanaged > >> gigabit switch, and 100 Mbps NICs on the clients. > >> > >> With flow control on, the server is limited to sending 100 Mbps to all > >> the clients. So with 10 thin clients the server can concurrently send > >> only 10 Mbps to each one of them. > >> > >> On NICs that support it, we turn flow control off and the server can > >> properly send 100 Mbps to each client, i.e. 1 Gbps to 10 clients. > >> > >> * Is there any way to bypass that problem on NICs that do not support > >> turning off flow control, like e.g. realteks? > >> I.e. when a client sends a pause signal to the server, instead of the > >> server pausing, to continue sending data to another client? > >> Or even to limit the amound of data the server sends to each client, > >> so that the clients never have to send pause signals? > >> > > > > You could set up QoS rules on the server to limit the network speed per client.. > > > >> * I really don't understand why flow control is enabled by default on > >> NICs and switches. In which case does it help? As far as I > >> understand, all it does is ruin gigabit => 100 Mbps connections... > >> > >> * As a side note, since rtl8169 is a very common chipset, is there a > >> way to disable flow control for that specific NIC? > >> > >> This problem affects thousands of LTSP installations, we'd much > >> appreciate your knowledge and feedback on it. > >> > > > > Did you try disabling flow control from the switch? > > He stated the switch was a un-managed switch, so he would be unable to disable flow control on the switch. > Oh, I missed that :) Never mind then. -- Pasi -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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