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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: PM policy, hotplug, power saving (was Re: [PATCH] b44: power down PHY when interface down)
On Sat, 30 Jun 2007 12:42:06 -0400 Jeff Garzik <[EMAIL PROTECTED]> wrote: > Arjan van de Ven wrote: > > Matthew Garrett wrote: > >> Do you still get link beat detection when the phy is powered down? > > > does that matter? > > If the interface is down, nic drivers aren't expected to detect link... > > if userspace wants to find link status it should have the interface up. > > > 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. > > Jeff We do have IFF_DORMANT, but almost no driver uses it. And most certainly, the common applications wouldn't know how to use it. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
PM policy, hotplug, power saving (was Re: [PATCH] b44: power down PHY when interface down)
Arjan van de Ven wrote: Matthew Garrett wrote: Do you still get link beat detection when the phy is powered down? does that matter? If the interface is down, nic drivers aren't expected to detect link... if userspace wants to find link status it should have the interface up. 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. Jeff - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
