mdoc(7) police: tidy up.

share/man/man4/polling.4

@@ -8,83 +8,104 @@
 .Nm polling
 .Nd device polling support
 .Sh SYNOPSIS
-.Cd options DEVICE_POLLING
-.Cd options HZ=1000
+.Cd "options DEVICE_POLLING"
+.Cd "options HZ=1000"
 .Sh DESCRIPTION
-"Device polling" (polling for brevity) refers to a technique to
+.Dq "Device polling"
+(polling for brevity) refers to a technique to
 handle devices that does not rely on the latter to generate
 interrupts when they need attention, but rather lets the CPU poll
 devices to service their needs.
 This might seem inefficient and counterintuitive, but when done
-properly, polling gives more control to the operating system on
+properly,
+.Nm
+gives more control to the operating system on
 when and how to handle devices, with a number of advantages in terms
 of system responsivity and performance.
 .Pp
-In particular, polling reduces the overhead for context
+In particular,
+.Nm
+reduces the overhead for context
 switches which is incurred when servicing interrupts, and
 gives more control on the scheduling of the CPU between various
 tasks (user processes, software interrupts, device handling)
 which ultimately reduces the chances of livelock in the system.
-
 .Sh PRINCIPLES OF OPERATION
-
 In the normal, interrupt-based mode, devices generate an interrupt
-whenever they need attention. This in turn causes a
+whenever they need attention.
+This in turn causes a
 context switch and the execution of a interrupt handler
 which performs whatever processing is needed by the device.
 The duration of the interrupt handler is potentially unbounded
 unless the device driver has been programmed with real-time
-concerns in mind (which is generally not the case for FreeBSD
-drivers). Furthermore, under heavy traffic, the system might be
+concerns in mind (which is generally not the case for
+.Fx
+drivers).
+Furthermore, under heavy traffic, the system might be
 persistently processing interrupts without being able to
 complete other work, either in the kernel or in userland.
 .Pp
-Polling disables interrupts by polling devices at appropriate
-times, i.e. on clock interrupts, system calls and within the idle loop.
-This way, the context switch overhead is removed. Furthermore,
+.Nm Polling
+disables interrupts by polling devices at appropriate
+times, i.e., on clock interrupts, system calls and within the idle loop.
+This way, the context switch overhead is removed.
+Furthermore,
 the operating system can control accurately how much work to spend
 in handling device events, and thus prevent livelock by reserving
 some amount of CPU to other tasks.
 .Pp
-Polling is enabled with a sysctl variable
+.Nm Polling
+is enabled with a
+.Xr sysctl 8
+variable
 .Va kern.polling.enable
 whereas the percentage of CPU cycles reserved to userland processes is
-controlled by the sysctl variable
+controlled by the
+.Xr sysctl 8
+variable
 .Va kern.polling.user_frac
 whose range is 0 to 100 (50 is the default value).
 .Pp
-When polling is enabled, and provided that there is work to do,
+When
+.Nm
+is enabled, and provided that there is work to do,
 up to
-.Va user_frac
+.Va kern.polling.user_frac
 percent of the CPU cycles is reserved to userland tasks, the
 remaining fraction being available for device processing.
 .Pp
-Enabling polling also changes the way network software interrupts
+Enabling
+.Nm
+also changes the way network software interrupts
 are scheduled, so there is never the risk of livelock because
 packets are not processed to completion.
 .Pp
 There are other variables which control or monitor the behaviour
 of devices operating in polling mode, but they are unlikely to
 require modifications, and are documented in the source file
-.Nm src/sys/kern/kern_poll.c
+.Pa sys/kern/kern_poll.c .
 .Sh SUPPORTED DEVICES
-
-Polling requires explicit modifications to the device drivers.
+.Nm Polling
+requires explicit modifications to the device drivers.
 As of this writing, the
-.Li "dc", "fxp"
+.Xr dc 4 ,
+.Xr fxp 4 ,
 and
-.Li "sis"
+.Xr sis 4
 devices are supported, with other 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
+and writing a callback function,
+.Fn *_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.
 .Pp
 Because in the worst case devices are only polled on
 clock interrupts, in order to reduce the latency in processing
-packets it is advisable to increase the frequency of the clock
+packets, it is advisable to increase the frequency of the clock
 to at least 1000 HZ.
 .Sh HISTORY
 Device polling was introduced in February 2002 by