Michael Ernest
2011-Jan-05 17:30 UTC
[dtrace-discuss] dtrace-discuss Digest, Vol 69, Issue 2
Hello Srikant -
A quantization distributes the results of your aggregation into ranges
ordered by a power-of-two. Presumably what you''d do in your script is
capture the inclusive elapsed time of each function call in your library,
then use this quantization to see how tightly-banded the times are. Perhaps
there''s some blocking I/O in some of your calls, for example, in which
case
you might expect a wide difference with functions that don''t.
I''ve annotated your code to show what you''re actually doing:
pid$1:libswduar::entry
{
// Associative array indexing timestamps by function call
duarEntry[probefunc] = timestamp;
// Aggregation to count each function invoked
@duarCount[probefunc] = count();
}
pid$1:libswduar::return
{
// Compute elapsed time in milliseconds
this->elapsed = (timestamp - duarEntry[probefunc])/1000000;
// Quantize elapsed time per function call
@totduarTime[probefunc] = quantize(this->elapsed);
// Zero out array element
duarEntry[probefunc] = 0;
}
That said, your output doesn''t make sense, unless you are in fact
waiting 2
billion-plus milliseconds on 21 of your LDAP searches. Or maybe you''re
using
ActiveDirectory. Joking aside, I''d guess the problem is that the trace
code
assumes a single-threaded, single-CPU model. A more general solution tracks
each function call by thread:
pid$1:libswduar::entry
{
@duarCount[probefunc] = count();
}
On Wed, Jan 5, 2011 at 8:48 AM, <dtrace-discuss-request at
opensolaris.org>wrote:
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> 1. Understand the dtrace quantize output (RAMASUBRAMANIAN Srikant)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 5 Jan 2011 17:47:24 +0100
> From: RAMASUBRAMANIAN Srikant <Srikant.RAMASUBRAMANIAN at swift.com>
> To: "dtrace-discuss at opensolaris.org" <dtrace-discuss at
opensolaris.org>
> Subject: [dtrace-discuss] Understand the dtrace quantize output
> Message-ID:
>
> <1759DECB91276E4083D703A908840BE7E140DDED2A at
BE-EXCHANGE-10.swift.corp>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi,
>
>
>
> I am kind of new to DTrace , I have written a script to time function calls
> in our application library ,
>
>
>
> Wanted to know how to interpret the output from quantize of the elapsed
> time
> in each function call , here is a sample
>
>
>
> Here is the entry and return function for the library that is being traced
>
>
>
> pid$1:libswduar::entry
> {
> duarEntry[probefunc] = timestamp;
> @duarCount[probefunc] = count();
> }
>
> pid$1:libswduar::return
>
> {
> this->elapsed = (timestamp - duarEntry[probefunc])/1000000;
> @totduarTime[probefunc] = quantize(this->elapsed);
> duarEntry[probefunc] = 0;
> }
>
>
>
> LdapSearchRequest
>
>
>
> value ------------- Distribution ------------- count
>
> -1 | 0
>
> 0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 147
>
> 1 | 0
>
> 2 | 0
>
> 4 | 0
>
> 8 | 0
>
> 16 | 0
>
> 32 | 0
>
> 64 | 0
>
> 128 | 0
>
> 256 | 0
>
> 512 | 0
>
> 1024 | 0
>
> 2048 | 0
>
> 4096 | 0
>
> 8192 | 0
>
> 16384 | 0
>
> 32768 | 0
>
> 65536 | 0
>
> 131072 | 0
>
> 262144 | 0
>
> 524288 | 0
>
> 1048576 | 0
>
> 2097152 | 0
>
> 4194304 | 0
>
> 8388608 | 0
>
> 16777216 | 0
>
> 33554432 | 0
>
> 67108864 | 0
>
> 134217728 | 0
>
> 268435456 | 0
>
> 536870912 | 0
>
> 1073741824 | 0
>
> 2147483648 |@@@@@ 21
>
> 4294967296 | 0
>
>
>
> Thanks & Regards
>
> Srikant Ramasubramanian
> SWIFTNet Link
>
> Tel: + 1(703) - 365- 6117
>
> Fax: + 1(703) - 365 - 6410
>
> Company name (e.g. ''S.W.I.F.T. SCRL'' for users in BE)
>
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--
Michael Ernest
Inkling Research, Inc.
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