is enabled, and provided that there is some work to do,
up to this percent of the CPU cycles is reserved to userland tasks,
the remaining fraction being available for
Default is 50.
Maximum number of packets grabbed from each network interface in
each timer tick.
This number is dynamically adjusted by the kernel,
according to the programmed
CPU speed, and system load.
The burst above is split into smaller chunks of this number of
packets, going round-robin among all interfaces registered for
This prevents the case that a large burst from a single interface
can saturate the IP interrupt queue
Default is 5.
Upper bound for
Note that when
is enabled, each interface can receive at most
(HZ * burst_max)
packets per second unless there are spare CPU cycles available for
in the idle loop.
This number should be tuned to match the expected load
(which can be quite high with GigE cards).
Default is 150 which is adequate for 100Mbit network and HZ=1000.
is enabled in the idle loop.
There are no reasons (other than power saving or bugs in the schedulers
handling of idle priority kernel threads) to disable this.
Controls how often (every
reg_frac / HZ
seconds) the status registers of the device are checked for error
conditions and the like.
Increasing this value reduces the load on the bus, but also delays
the error detection.
Default is 20.
How many active devices have registered for
Legacy MIB, that was used to enable or disable polling globally.
Currently if set to 1,
is enabled on all capable interfaces.
If set to 0,
is disabled on all interfaces.
Device polling requires explicit modifications to the device drivers. As of this writing, the bge(4), dc(4), em(4), fwe(4), fwip(4), fxp(4), ixgb(4), nge(4), re(4), rl(4), sf(4), sis(4), ste(4), stge(4), vge(4), vr(4), and xl(4) devices are supported, with others in the works. The modifications are rather straightforward, consisting in the extraction of the inner part of the interrupt service routine and writing a callback function, *_poll, which is invoked to probe the device for events and process them. (See the conditionally compiled sections of the devices mentioned above for more details.)
As in the worst case the devices are only polled on clock interrupts, in order to reduce the latency in processing packets, it is not advisable to decrease the frequency of the clock below 1000 Hz.
Device polling first appeared in
.Fx 4.6 and
.Fx 5.0 .
Device polling was written by
.An Luigi Rizzo Aq email@example.com .
|December 2, 2006||POLLING (4)|