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diff --git a/share/doc/papers/kerntune/2.t b/share/doc/papers/kerntune/2.t new file mode 100644 index 000000000000..1a90ceb2a7ee --- /dev/null +++ b/share/doc/papers/kerntune/2.t @@ -0,0 +1,228 @@ +.\" Copyright (c) 1984 M. K. McKusick +.\" Copyright (c) 1984 The Regents of the University of California. +.\" All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.ds RH The \fIgprof\fP Profiler +.NH 1 +The \fIgprof\fP Profiler +.PP +The purpose of the \fIgprof\fP profiling tool is to +help the user evaluate alternative implementations +of abstractions. +The \fIgprof\fP design takes advantage of the fact that the kernel +though large, is structured and hierarchical. +We provide a profile in which the execution time +for a set of routines that implement an +abstraction is collected and charged +to that abstraction. +The profile can be used to compare and assess the costs of +various implementations [Graham82] [Graham83]. +.NH 2 +Data presentation +.PP +The data is presented to the user in two different formats. +The first presentation simply lists the routines +without regard to the amount of time their descendants use. +The second presentation incorporates the call graph of the +kernel. +.NH 3 +The Flat Profile +.PP +The flat profile consists of a list of all the routines +that are called during execution of the kernel, +with the count of the number of times they are called +and the number of seconds of execution time for which they +are themselves accountable. +The routines are listed in decreasing order of execution time. +A list of the routines that are never called during execution of +the kernel is also available +to verify that nothing important is omitted by +this profiling run. +The flat profile gives a quick overview of the routines that are used, +and shows the routines that are themselves responsible +for large fractions of the execution time. +In practice, +this profile usually shows that no single function +is overwhelmingly responsible for +the total time of the kernel. +Notice that for this profile, +the individual times sum to the total execution time. +.NH 3 +The Call Graph Profile +.PP +Ideally, we would like to print the call graph of the kernel, +but we are limited by the two-dimensional nature of our output +devices. +We cannot assume that a call graph is planar, +and even if it is, that we can print a planar version of it. +Instead, we choose to list each routine, +together with information about +the routines that are its direct parents and children. +This listing presents a window into the call graph. +Based on our experience, +both parent information and child information +is important, +and should be available without searching +through the output. +Figure 1 shows a sample \fIgprof\fP entry. +.KF +.DS L +.TS +box center; +c c c c c l l +c c c c c l l +c c c c c l l +l n n n c l l. + called/total \ \ parents +index %time self descendants called+self name index + called/total \ \ children +_ + 0.20 1.20 4/10 \ \ \s-1CALLER1\s+1 [7] + 0.30 1.80 6/10 \ \ \s-1CALLER2\s+1 [1] +[2] 41.5 0.50 3.00 10+4 \s-1EXAMPLE\s+1 [2] + 1.50 1.00 20/40 \ \ \s-1SUB1\s+1 <cycle1> [4] + 0.00 0.50 1/5 \ \ \s-1SUB2\s+1 [9] + 0.00 0.00 0/5 \ \ \s-1SUB3\s+1 [11] +.TE +.ce +Figure 1. Profile entry for \s-1EXAMPLE\s+1. +.DE +.KE +.PP +The major entries of the call graph profile are the entries from the +flat profile, augmented by the time propagated to each +routine from its descendants. +This profile is sorted by the sum of the time for the routine +itself plus the time inherited from its descendants. +The profile shows which of the higher level routines +spend large portions of the total execution time +in the routines that they call. +For each routine, we show the amount of time passed by each child +to the routine, which includes time for the child itself +and for the descendants of the child +(and thus the descendants of the routine). +We also show the percentage these times represent of the total time +accounted to the child. +Similarly, the parents of each routine are listed, +along with time, +and percentage of total routine time, +propagated to each one. +.PP +Cycles are handled as single entities. +The cycle as a whole is shown as though it were a single routine, +except that members of the cycle are listed in place of the children. +Although the number of calls of each member +from within the cycle are shown, +they do not affect time propagation. +When a child is a member of a cycle, +the time shown is the appropriate fraction of the time +for the whole cycle. +Self-recursive routines have their calls broken +down into calls from the outside and self-recursive calls. +Only the outside calls affect the propagation of time. +.PP +The example shown in Figure 2 is the fragment of a call graph +corresponding to the entry in the call graph profile listing +shown in Figure 1. +.KF +.DS L +.so fig2.pic +.ce +Figure 2. Example call graph fragment. +.DE +.KE +.PP +The entry is for routine \s-1EXAMPLE\s+1, which has +the Caller routines as its parents, +and the Sub routines as its children. +The reader should keep in mind that all information +is given \fIwith respect to \s-1EXAMPLE\s+1\fP. +The index in the first column shows that \s-1EXAMPLE\s+1 +is the second entry in the profile listing. +The \s-1EXAMPLE\s+1 routine is called ten times, four times by \s-1CALLER1\s+1, +and six times by \s-1CALLER2\s+1. +Consequently 40% of \s-1EXAMPLE\s+1's time is propagated to \s-1CALLER1\s+1, +and 60% of \s-1EXAMPLE\s+1's time is propagated to \s-1CALLER2\s+1. +The self and descendant fields of the parents +show the amount of self and descendant time \s-1EXAMPLE\s+1 +propagates to them (but not the time used by +the parents directly). +Note that \s-1EXAMPLE\s+1 calls itself recursively four times. +The routine \s-1EXAMPLE\s+1 calls routine \s-1SUB1\s+1 twenty times, \s-1SUB2\s+1 once, +and never calls \s-1SUB3\s+1. +Since \s-1SUB2\s+1 is called a total of five times, +20% of its self and descendant time is propagated to \s-1EXAMPLE\s+1's +descendant time field. +Because \s-1SUB1\s+1 is a member of \fIcycle 1\fR, +the self and descendant times +and call count fraction +are those for the cycle as a whole. +Since cycle 1 is called a total of forty times +(not counting calls among members of the cycle), +it propagates 50% of the cycle's self and descendant +time to \s-1EXAMPLE\s+1's descendant time field. +Finally each name is followed by an index that shows +where on the listing to find the entry for that routine. +.NH 2 +Profiling the Kernel +.PP +It is simple to build a 4.2BSD kernel that will automatically +collect profiling information as it operates simply by specifying the +.B \-p +option to \fIconfig\fP\|(8) when configuring a kernel. +The program counter sampling can be driven by the system clock, +or by an alternate real time clock. +The latter is highly recommended as use of the system clock results +in statistical anomalies in accounting for +the time spent in the kernel clock routine. +.PP +Once a profiling system has been booted statistic gathering is +handled by \fIkgmon\fP\|(8). +\fIKgmon\fP allows profiling to be started and stopped +and the internal state of the profiling buffers to be dumped. +\fIKgmon\fP can also be used to reset the state of the internal +buffers to allow multiple experiments to be run without +rebooting the machine. +The profiling data can then be processed with \fIgprof\fP\|(1) +to obtain information regarding the system's operation. +.PP +A profiled system is about 5-10% larger in its text space because of +the calls to count the subroutine invocations. +When the system executes, +the profiling data is stored in a buffer that is 1.2 +times the size of the text space. +All the information is summarized in memory, +it is not necessary to have a trace file +being continuously dumped to disk. +The overhead for running a profiled system varies; +under normal load we see anywhere from 5-25% +of the system time spent in the profiling code. +Thus the system is noticeably slower than an unprofiled system, +yet is not so bad that it cannot be used in a production environment. +This is important since it allows us to gather data +in a real environment rather than trying to +devise synthetic work loads. |