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Date: Sun, 1 Jul 2007 00:51:15 -0400 From: Kyle Moffett <mrmacman_g4@....com> To: Jeff Garzik <jeff@...zik.org> Cc: Arjan van de Ven <arjan@...ux.intel.com>, Matthew Garrett <mjg59@...f.ucam.org>, Török Edvin <edwintorok@...il.com>, netdev@...r.kernel.org, power@...host.org, zambrano@...adcom.com, linux-kernel@...r.kernel.org Subject: Re: PM policy, hotplug, power saving (was Re: [PATCH] b44: power down PHY when interface down) On Jun 30, 2007, at 12:42:06, Jeff Garzik wrote: > Definitely matters. Switch renegotiation can take a while, and you > must take into account the common case of interface bouncing > (immediate down, then up). > > Hoards actively complained the few times we experimented with this, > because of e.g. DHCP's habit of bouncing the interface, which > resulted in PHY power bouncing, which resulted in negotiation, > which resulted in an excrutiating wait on various broken or stupid > switches. > > Overall, this may be classed with other problems of a similar > sort: we can power down a PHY, but that removes hotplug capability > and extends partner/link negotiation time. > > Like SATA, we actually want to support BOTH -- active hotplug and > PHY power-down -- and so this wanders into power management policy. > > Give me a knob, and we can program plenty of ethernet|SATA|USB|... > drivers to power down the PHY and save power. With some buggy switches and other hardware you actually *want* to bounce the link to get them to properly renegotiate. I can also see wanting to power off and on a single-PoE-port NIC to restart whatever device is at the other end, although I don't know if any such devices exist. Currently the tg3 driver turns the PHY off and on during down/ up on a few of my systems, which I use to make a buggy no-name switch recognize STP changes properly. Cheers, Kyle Moffett - 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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