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Feature #570

lttng-tools 2.2.0-rc2: enable-channel man pages ought to mention minimum sub-buffer sizes

Added by Daniel U. Thibault almost 7 years ago. Updated about 6 years ago.

Status:
Resolved
Priority:
Normal
Assignee:
-
Target version:
Start date:
06/25/2013
Due date:
% Done:

0%

Estimated time:

Description

It seems the minimum size of the LTTng sub-buffers is 4096 bytes (for either domain and either buffering scheme):

$ sudo -H lttng create s
Session s created.
Traces will be written in /root/lttng-traces/s-20130625-101152
$ sudo -H lttng enable-channel k1 -k --subbuf-size 131072
Kernel channel k1 enabled for session s
$ sudo -H lttng enable-channel k2 -k --subbuf-size 65536
Kernel channel k2 enabled for session s
$ sudo -H lttng enable-channel k3 -k --subbuf-size 32768
Kernel channel k3 enabled for session s
$ sudo -H lttng enable-channel k4 -k --subbuf-size 16384
Kernel channel k4 enabled for session s
$ sudo -H lttng enable-channel k5 -k --subbuf-size 8192
Kernel channel k5 enabled for session s
$ sudo -H lttng enable-channel k6 -k --subbuf-size 4096
Kernel channel k6 enabled for session s
$ sudo -H lttng enable-channel k7 -k --subbuf-size 2048
PERROR [20531/20631]: ioctl kernel create channel: Invalid argument (in kernel_create_channel() at kernel.c:144)
Error: Channel k7: Kernel create channel failed (session s)
Warning: Some command(s) went wrong
$ sudo -H lttng create ss
Session ss created.
Traces will be written in /root/lttng-traces/ss-20130625-101446
$ sudo -H lttng enable-channel k7 -k --subbuf-size 2048
PERROR [20531/20631]: ioctl kernel create channel: Invalid argument (in kernel_create_channel() at kernel.c:144)
Error: Channel k7: Kernel create channel failed (session ss)
Warning: Some command(s) went wrong
$ sudo -H lttng enable-channel u7 -u --subbuf-size 2048
Error: Channel u7: Invalid parameter (session ss)
Warning: Some command(s) went wrong
$ sudo -H lttng enable-channel u6 -u --subbuf-size 4096
UST channel u6 enabled for session ss

This should be mentioned in the man pages.

#1

Updated by David Goulet almost 7 years ago

Unfortunately, this varies on the system. The page size is used to be the
minimum possible.

However, we can mention that and a way to find out like using

  1. getconf PAGESIZE

Once I'm able to log in, I'll switch that to 2.2 target and in Bug.

Thanks!

#2

Updated by David Goulet about 6 years ago

  • Status changed from New to Resolved
  • Target version set to 2.3

Currently fixed in 2.3.


          --subbuf-size SIZE
             Subbuffer size in bytes {+k,+M,+G}.  (default UST  uid:  131072,  UST  pid:
             4096, kernel: 262144, metadata: 4096) Rounded up to the next power of 2.

             The  minimum  subbuffer size, for each tracer, is the max value between the
             default above and the system page size. You can issue this command  to  get
             the current page size on your system: $ getconf PAGE_SIZE

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