[ oprofile-Bugs-615087 ] Samples with count=0 waste buffer space

[<no...@so...>]

Bugs item #615087, was opened at 2002-09-26 19:39
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=116191&aid=615087&group_id=16191

Category: None
Group: None
Status: Open
>Resolution: Fixed
Priority: 5
Submitted By: Bob Montgomery (mudbone)
Assigned to: Nobody/Anonymous (nobody)
Summary: Samples with count=0 waste buffer space

Initial Comment:
dump_one creates leaves entries with pid and eip intact, but zeroes the count.
evict_op_entry will copy anything with a non-zero eip to the buffer.  In combination,
they can send lots of samples to the buffer with count==0. 

It's probably useful for dump_one to allow the entry to retain its eip and
pid to reduce future thrashing (an entry that has hits will probably get more hits
after it's dumped).  So I think the best way to prevent 0-hit samples in
the buffer is to change the test in evict_op_entry from eip to counts.

For prospect's use of oprofile (we dump every two seconds), this cut the
number of 0-hit samples in half for a 1500 Hz profile of a kernel build.

Something like this:
diff -urN -X dontdiff oprofile/module/oprofile.c oprofile-25sep-play/module/oprofile.c
--- oprofile/module/oprofile.c	Thu Sep 26 11:16:45 2002
+++ oprofile-25sep-play/module/oprofile.c	Thu Sep 26 11:20:33 2002
@@ -69,8 +69,8 @@
 inline static void evict_op_entry(uint cpu, struct _oprof_data * data,
 	struct op_sample const * ops, long eflags)
 {
-	/* ignore initial hash table cleanout */
-	if (ops->eip == 0)
+	/* ignore op_samples with no hits (initial value or recently dumped) */
+	if (ops->count == 0)
 		return;
  
 	memcpy(&data->buffer[data->nextbuf], ops, sizeof(struct op_sample));




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https://sourceforge.net/tracker/?func=detail&atid=116191&aid=615087&group_id=16191