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bmake inefficiencies

I had a look with truss at what bmake is doing and I think a lot of
the syscalls can be easily avoided. Examples come from FreeBSD with
bmake-20210110 and I don't know to what extent they are representative
for other systems.

1. spurious waitpid

when doing buildkernel I counted the following:
7010 cases of error code 0 (== nothing to do)
371 cases of ECHILD
1526 cases of reaping

To my understanding bmake knows when there are any children to reap
and at least the first case can be easily avoided.


for example mkstemp is used and FD_CLOEXEC performed on the result.
Instead mkostemp can be used and mkTempFile can accept O_CLOEXEC as an
argument to save explicit fcntl.

3. avoidable temp files

JobOpenTmpFile opens a file and later checks if anything was written
to it. Not an actual patch, but a hack to demonstrate the fix can be
found at the end. Looks like checking can be done upfront in O(1) time
(not done in the patch below).

With this in place I get the following result for buildworld:
87930 JobOpenTmpFile: created!
70564 JobOpenTmpFile: skipped!

i.e. about 44% of all temp files can be avoided at least in this workload.

There is probably more, but I did not want to analyze further.

Is this something you can address?


diff --git a/contrib/bmake/job.c b/contrib/bmake/job.c
index d43761ca80ff..67b75f228547 100644
--- a/contrib/bmake/job.c
+++ b/contrib/bmake/job.c
@@ -1022,6 +1022,24 @@ JobPrintCommand(Job *job, ShellWriter *wr,
StringListNode *ln, const char *ucmd)
  * Return whether at least one command was written to the shell file.
+static Boolean
+JobWillPrintCommands(Job *job)
+       StringListNode *ln;
+       Boolean seen = FALSE;
+       for (ln = job->node->commands.first; ln != NULL; ln = ln->next) {
+               const char *cmd = ln->datum;
+               if (strcmp(cmd, "...") == 0) {
+                       break;
+               }
+               seen = TRUE;
+       }
+       return seen;
 static Boolean
 JobPrintCommands(Job *job)
@@ -1609,6 +1627,15 @@ JobOpenTmpFile(Job *job, GNode *gn, Boolean
cmdsOK, Boolean *out_run)

+       if (getenv("MAKE_TRYSKIP") != NULL) {
+               if (!JobWillPrintCommands(job)) {
+                       printf("%s: skipped!\n", __func__);
+                       *out_run = FALSE;
+                       return;
+               }
+               printf("%s: created!\n", __func__);
+       }
        tfd = mkTempFile(TMPPAT, &tfile);
        if (!DEBUG(SCRIPT))


Mateusz Guzik <mjguzik>

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