perf_event_open.2: Minor grammar, formatting, wording, and typo fixes

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/perf_event_open.2

@@ -97,13 +97,13 @@ when running on the specified CPU.
 .TP
 .BR "pid == \-1" " and " "cpu >= 0"
 This measures all processes/threads on the specified CPU.
-Measurements such as this require the
+This requires
 .B CAP_SYS_ADMIN
 capability or a
 .I /proc/sys/kernel/perf_event_paranoid
 value of less than 1.
 .TP
-.BR pid==\-1 " and " cpu==\-1
+.BR "pid == \-1" " and " "cpu == \-1"
 This setting is invalid and will return an error.
 .P
 The
@@ -124,7 +124,7 @@ An event group is scheduled onto the CPU as a unit: it will
 be put onto the CPU only if all of the events in the group can be put onto
 the CPU.
 This means that the values of the member events can be
-meaningfully compared, added, divided (to get ratios), and so on, with each
+meaningfully compared\(emadded, divided (to get ratios), and so on\(emwith each
 other, since they have counted events for the same set of executed
 instructions.
 .P
@@ -161,7 +161,7 @@ This flag reroutes the output from an event to the group leader.
 .BR PERF_FLAG_PID_CGROUP " (since Linux 2.6.39)."
 This flag activates per-container system-wide monitoring.
 A container
-is an abstraction that isolates a set of resources for finer grain
+is an abstraction that isolates a set of resources for finer-grained
 control (CPUs, memory, etc.).
 In this mode, the event is measured
 only if the thread running on the monitored CPU belongs to the designated
@@ -1262,7 +1262,7 @@ struct perf_event_mmap_page {
 .fi
 .in
 
-The following looks at the fields in the
+The following list describes the fields in the
 .I perf_event_mmap_page
 structure in more detail:
 .TP
@@ -1432,13 +1432,16 @@ If
 is set, then the hardware clock (the TSC timestamp counter on x86)
 can be calculated from the
 .IR time_zero ", " time_mult ", and " time_shift " values:"
+
 .nf
     time = timestamp - time_zero;
     quot = time / time_mult;
     rem  = time % time_mult;
     cyc = (quot << time_shift) + (rem << time_shift) / time_mult;
 .fi
+
 And vice versa:
+
 .nf
     quot = cyc >> time_shift;
     rem  = cyc & ((1 << time_shift) - 1);
@@ -1452,7 +1455,9 @@ The value continuously increases, it does not wrap.
 The value needs to be manually wrapped by the size of the mmap buffer
 before accessing the samples.
 
-On SMP-capable platforms, after reading the data_head value,
+On SMP-capable platforms, after reading the
+.I data_head
+value,
 user space should issue an rmb().
 .TP
 .I data_tail
@@ -2146,10 +2151,10 @@ to calculate event values can be found in that section.
 .PP
 Various ioctls act on
 .BR perf_event_open ()
-file descriptors
+file descriptors:
 .TP
 .B PERF_EVENT_IOC_ENABLE
-Enables the individual event or event group specified by the
+This enables the individual event or event group specified by the
 file descriptor argument.
 
 If the
@@ -2159,7 +2164,7 @@ enabled, even if the event specified is not the group leader
 (but see BUGS).
 .TP
 .B PERF_EVENT_IOC_DISABLE
-Disables the individual counter or event group specified by the
+This disables the individual counter or event group specified by the
 file descriptor argument.
 
 Enabling or disabling the leader of a group enables or disables the
@@ -2234,7 +2239,7 @@ This adds an ftrace filter to this event.
 The argument is a pointer to the desired ftrace filter.
 .TP
 .BR PERF_EVENT_IOC_ID " (since Linux 3.12)"
-Returns the event ID value for the given event fd.
+This returns the event ID value for the given event fd.
 
 The argument is a pointer to a 64-bit unsigned integer
 to hold the result.
@@ -2288,14 +2293,15 @@ The default value is
 .TP
 .I /proc/sys/kernel/perf_event_mlock_kb
 
-Maximum number of pages an unprivileged user can mlock (2) .
+Maximum number of pages an unprivileged user can
+.BR mlock (2).
 The default is 516 (kB).
 
 .RE
 Files in
 .I /sys/bus/event_source/devices/
 .RS 4
-Since Linux 2.6.34 the kernel supports having multiple PMUs
+Since Linux 2.6.34, the kernel supports having multiple PMUs
 available for monitoring.
 Information on how to program these PMUs can be found under
 .IR /sys/bus/event_source/devices/ .
@@ -2304,7 +2310,9 @@ Each subdirectory corresponds to a different PMU.
 .IR /sys/bus/event_source/devices/*/type " (since Linux 2.6.38)"
 This contains an integer that can be used in the
 .I type
-field of perf_event_attr to indicate you wish to use this PMU.
+field of
+.I perf_event_attr
+to indicate that you wish to use this PMU.
 .TP
 .IR /sys/bus/event_source/devices/*/rdpmc " (since Linux 3.4)"
 If this file is 1, then direct user-space access to the
@@ -2315,7 +2323,9 @@ This can be disabled by echoing 0 to the file.
 This subdirectory contains information on the architecture-specific
 subfields available for programming the various
 .I config
-fields in the perf_event_attr struct.
+fields in the
+.I perf_event_attr
+struct.
 
 The content of each file is the name of the config field, followed
 by a colon, followed by a series of integer bit ranges separated by
@@ -2325,7 +2335,8 @@ For example, the file
 may contain the value
 .I config1:1,6-10,44
 which indicates that event is an attribute that occupies bits 1,6-10, and 44
-of perf_event_attr::config1.
+of
+.IR perf_event_attr::config1 .
 .TP
 .IR /sys/bus/event_source/devices/*/events/ " (since Linux 3.4)"
 This subdirectory contains files with predefined events.
@@ -2370,7 +2381,8 @@ can be inconsistent, and may
 vary across processor architectures and performance monitoring units.
 .TP
 .B E2BIG
-Returned if the perf_event_attr
+Returned if the
+.I perf_event_attr
 .I size
 value is too small
 (smaller than
@@ -2379,7 +2391,8 @@ too big (larger than the page size),
 or larger than the kernel supports and the extra bytes are not zero.
 When
 .B E2BIG
-is returned, the perf_event_attr
+is returned, the
+.I perf_event_attr
 .I size
 field is overwritten by the kernel to be the size of the structure
 it was expecting.
@@ -2522,7 +2535,7 @@ option to
 is needed to properly get overflow signals in threads.
 This was introduced in Linux 2.6.32.
 
-Prior to Linux 2.6.33 (at least for x86) the kernel did not check
+Prior to Linux 2.6.33 (at least for x86), the kernel did not check
 if events could be scheduled together until read time.
 The same happens on all known kernels if the NMI watchdog is enabled.
 This means to see if a given set of events works you have to
@@ -2530,11 +2543,11 @@ This means to see if a given set of events works you have to
 start, then read before you know for sure you
 can get valid measurements.
 
-Prior to Linux 2.6.34 event constraints were not enforced by the kernel.
+Prior to Linux 2.6.34, event constraints were not enforced by the kernel.
 In that case, some events would silently return "0" if the kernel
 scheduled them in an improper counter slot.
 
-Prior to Linux 2.6.34 there was a bug when multiplexing where the
+Prior to Linux 2.6.34, there was a bug when multiplexing where the
 wrong results could be returned.
 
 Kernels from Linux 2.6.35 to Linux 2.6.39 can quickly crash the kernel if