Project

General

Profile

Actions
Copy link

Bug #228

closed
MK

Subbuffer sizes and powers of 2

Bug #228: Subbuffer sizes and powers of 2

Added by Matthew Khouzam about 14 years ago. Updated about 13 years ago.

Status:
Resolved
Priority:
Normal
Assignee:
-
Target version:
LTTng - 2.2
Start date:
04/26/2012
Due date:
% Done:

0%

Estimated time:

Description

A subbuffer should be able to take any value, it is unreasonable to ask a user in userland to memorize the powers of 2 greater than 16.

A good compromise would be to cause lttng tool to create subbuffers that are rounded up to the nearest power of 2. I can personnaly garanty that a user asking for 1000000 bytes per subbuffer will not be outraged if the buffer is in reality 1024^2.

Another useful thing would be to have human friendly input like 4k 16k 1m 2g...

Files

0001-Make-subbufer-size-always-take-next-power-of-2-for-a.patch (1.44 KB) 0001-Make-subbufer-size-always-take-next-power-of-2-for-a.patch patch Matthew Khouzam, 09/21/2012 04:11 PM

Related issues 1 (0 open — 1 closed)

Related to LTTng-tools - Bug #235: lttng_enable_channel with too little subbuffers size returns an error that isn't explicitResolved05/08/2012

Actions

MD Updated by Mathieu Desnoyers about 14 years ago Actions
Copy link
 #1

Issue #228 has been reported by Matthew Khouzam.

----------------------------------------
Bug #228: Subbuffer sizes and powers of 2
https://bugs.lttng.org/issues/228

Author: Matthew Khouzam
Status: New
Priority: Normal
Assignee:
Category:
Target version:

A subbuffer should be able to take any value, it is unreasonable to ask a user in userland to memorize the powers of 2 greater than 16.

A good compromise would be to cause lttng tool to create subbuffers that are rounded up to the nearest power of 2. I can personnaly garanty that a user asking for 1000000 bytes per subbuffer will not be outraged if the buffer is in reality 1024^2.

Another useful thing would be to have human friendly input like 4k 16k 1m 2g...

Agreed, this should be done in lttng cmd line tool. Patch is welcome,

Thanks,

Mathieu

--
You have received this notification because you have either subscribed to it, or are involved in it.
To change your notification preferences, please click here: http://bugs.lttng.org/my/account

--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com

YB Updated by Yannick Brosseau almost 14 years ago Actions
Copy link
 #2

  • Target version set to 2.1 pre

YB Updated by Yannick Brosseau over 13 years ago Actions
Copy link
 #3

  • Target version deleted (2.1 pre)

It might also be an helper function (in the lib) that do the round up

-- edited to add (in the lib)

MD Updated by Mathieu Desnoyers over 13 years ago Actions
Copy link
 #5

Please implement by pulling lttng-ust libringbuffer/backend_internal.h get_count_order() into lttng-tools. This code is already tested, and FWIW more efficient than the patch you proposed. Moreover, it follows the project coding style.

Thanks,

Mathieu

MK Updated by Matthew Khouzam over 13 years ago Actions
Copy link
 #6

That's a pretty cool function. What is a FLS? I can tell the lttng_ust_fls() function is more desirable for this than get_count_order since if we give ti a subbuffer of 2^n, we don't need to allocate 2^n+1... or do we?

Also, the only comments are "arch-agnostic implementation" event though that is great to know, I think we really need to know what is a fls even more and what get_count_order does.

MD Updated by Mathieu Desnoyers over 13 years ago Actions
Copy link
 #7

Issue #228 has been updated by Matthew Khouzam.

That's a pretty cool function. What is a FLS? I can tell the lttng_ust_fls() function is more desirable for this than get_count_order since if we give ti a subbuffer of 2^n, we don't need to allocate 2^n+1... or do we?

Also, the only comments are "arch-agnostic implementation" event though that is great to know, I think we really need to know what is a fls even more and what get_count_order does.

fls = find last bit set. There is a similar implementation in the Linux
kernel, so you can find its documentation there.

fls has corner-cases with the exact power values: it's not the semantic
we need. We want get_count_order. get_count_order, if given 2^n, returns
2^n, not 2^(n+1) like you assume.

Thanks,

Mathieu

----------------------------------------
Bug #228: Subbuffer sizes and powers of 2
https://bugs.lttng.org/issues/228#change-775

Author: Matthew Khouzam
Status: New
Priority: Normal
Assignee:
Category:
Target version:

A subbuffer should be able to take any value, it is unreasonable to ask a user in userland to memorize the powers of 2 greater than 16.

A good compromise would be to cause lttng tool to create subbuffers that are rounded up to the nearest power of 2. I can personnaly garanty that a user asking for 1000000 bytes per subbuffer will not be outraged if the buffer is in reality 1024^2.

Another useful thing would be to have human friendly input like 4k 16k 1m 2g...

--
You have received this notification because you have either subscribed to it, or are involved in it.
To change your notification preferences, please click here: http://bugs.lttng.org/my/account

--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com

DG Updated by David Goulet over 13 years ago Actions
Copy link
 #8

  • Status changed from New to Confirmed
  • Target version set to 2.2

I'm +1 to adding a helper call in liblttng-ctl rather than hacking the values behind the user back.

Flagging this for 2.2. Anyone want to contribute, feel free! :)

MD Updated by Mathieu Desnoyers about 13 years ago Actions
Copy link
 #9

  • Status changed from Confirmed to Resolved
commit 16068db5dda7041571a5520dc69c96af43b799a2
Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date:   Thu May 2 11:53:08 2013 -0400

    Fix: check errors in lttng command argument values

    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

commit 8ce58badbfbff17e050194e01a9120ac6058bc1c
Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date:   Thu May 2 11:33:46 2013 -0400

    Implement get_count_order in lttng utils

    Imported from Userspace RCU rculfhash.c.

    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Actions
Copy link

Also available in: PDF Atom