[[project @ 2003-01-10 16:10:00 by simonpj]
simonpj**20030110161000
Add notes on real-time profiling from Jan-Willhem
] {
hunk ./ghc/docs/users_guide/profiling.sgml 846
+
+
+
+
hunk ./ghc/docs/users_guide/profiling.sgml 1071
+
+
+
+ Manipulating the hp file
+
+(Notes kindly offered by Jan-Willhem Maessen.)
+
+
+The FOO.hp file produced when you ask for the
+heap profile of a program FOO is a text file with a particularly
+simple structure. Here's a representative example, with much of the
+actual data omitted:
+
+JOB "FOO -hC"
+DATE "Thu Dec 26 18:17 2002"
+SAMPLE_UNIT "seconds"
+VALUE_UNIT "bytes"
+BEGIN_SAMPLE 0.00
+END_SAMPLE 0.00
+BEGIN_SAMPLE 15.07
+ ... sample data ...
+END_SAMPLE 15.07
+BEGIN_SAMPLE 30.23
+ ... sample data ...
+END_SAMPLE 30.23
+... etc.
+BEGIN_SAMPLE 11695.47
+END_SAMPLE 11695.47
+
+The first four lines (JOB, DATE, SAMPLE_UNIT, VALUE_UNIT) form a
+header. Each block of lines starting with BEGIN_SAMPLE and ending
+with END_SAMPLE forms a single sample (you can think of this as a
+vertical slice of your heap profile). The hp2ps utility should accept
+any input with a properly-formatted header followed by a series of
+*complete* samples.
+
+
+
+
+ Zooming in on regions of your profile
+
+
+You can look at particular regions of your profile simply by loading a
+copy of the .hp file into a text editor and deleting the unwanted
+samples. The resulting .hp file can be run through hp2ps and viewed
+or printed.
+
+
+
+
+ Viewing the heap profile of a running program
+
+
+The .hp file is generated incrementally as your
+program runs. In principle, running hp2ps on the incomplete file
+should produce a snapshot of your program's heap usage. However, the
+last sample in the file may be incomplete, causing hp2ps to fail. If
+you are using a machine with UNIX utilities installed, it's not too
+hard to work around this problem (though the resulting command line
+looks rather Byzantine):
+
+ head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \
+ | hp2ps > FOO.ps
+
+
+The command fgrep -n END_SAMPLE FOO.hp finds the
+end of every complete sample in FOO.hp, and labels each sample with
+its ending line number. We then select the line number of the last
+complete sample using tail and cut. This is used as a
+parameter to head; the result is as if we deleted the final
+incomplete sample from FOO.hp. This results in a properly-formatted
+.hp file which we feed directly to hp2ps.
+
+
+
+ Viewing a heap profile in real time
+
+
+The gv and ghostview programs
+have a "watch file" option can be used to view an up-to-date heap
+profile of your program as it runs. Simply generate an incremental
+heap profile as described in the previous section. Run gv on your
+profile:
+
+ gv -watch -seascape FOO.ps
+
+If you forget the -watch flag you can still select
+"Watch file" from the "State" menu. Now each time you generate a new
+profile FOO.ps the view will update automatically.
+
+
+
+This can all be encapsulated in a little script:
+
+ #!/bin/sh
+ head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \
+ | hp2ps > FOO.ps
+ gv -watch -seascape FOO.ps &
+ while [ 1 ] ; do
+ sleep 10 # We generate a new profile every 10 seconds.
+ head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \
+ | hp2ps > FOO.ps
+ done
+
+Occasionally gv will choke as it tries to read an incomplete copy of
+FOO.ps (because hp2ps is still running as an update
+occurs). A slightly more complicated script works around this
+problem, by using the fact that sending a SIGHUP to gv will cause it
+to re-read its input file:
+
+ #!/bin/sh
+ head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \
+ | hp2ps > FOO.ps
+ gv FOO.ps &
+ gvpsnum=$!
+ while [ 1 ] ; do
+ sleep 10
+ head -`fgrep -n END_SAMPLE FOO.hp | tail -1 | cut -d : -f 1` FOO.hp \
+ | hp2ps > FOO.ps
+ kill -HUP $gvpsnum
+ done
+
+
+
+
+
}