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From: Steven Rostedt <rostedt@goodmis.org>
To: sameeruddin shaik <sameeruddin.shaik8@gmail.com>
Cc: linux-trace-devel@vger.kernel.org
Subject: Re: [PATCH 08/13 v2] libtracefs: Allow for setting filters with regex expressions
Date: Wed, 31 Mar 2021 22:41:30 -0400
Message-ID: <20210331224130.4fec9cf5@oasis.local.home> (raw)
In-Reply-To: <fa1cb382-5984-d5de-5905-0eb3fd45a697@gmail.com>

On Fri, 2 Apr 2021 07:29:59 +0530
sameeruddin shaik <sameeruddin.shaik8@gmail.com> wrote:

> >
> > If you left off the "^" and "$" then it would be a glob, where "*" means
> > zero or more of any character. But if you want the same in regex, you need
> > to use:
> >
> >   "^ext4.*$"  
> 
> IF we use the regex in filters, running time of the program is 
> increasing drastically.

Only if the kernel doesn't support indexing, then it would take less
than a second.

> 
> lets say,
> 
> if we give the kernel glob as a filter, its getting converted to regex 
> and running time of program is
> 
> 5 secs, in other case where we use regex, its taking 80 secs to complete.

What example did you use? And yes, regex would do the matching in user
space and globs would be processed in the kernel (unless indexing is
available, in which case it uses regex for everything). That's because
the globs in the kernel were created to speed up the selection of
multiple functions. The regex would pass in one function that matched
at a time, and that's more of a O(n^2) algorithm.

This is why the function supports both globs and regex.

For simple regex, we could optimize it to use a glob, if indexing is
not supported. I mentioned this to Tzvetomir before and we agreed that
this optimization can be done with later patches in the future, as
modern kernels (5.1 and beyond) support indexing.

-- Steve

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-30  0:51 [PATCH 00/13 v2] libtracefs: Add tracefs_function_filter() Steven Rostedt
2021-03-30  0:51 ` [PATCH 01/13 v2] libtracefs: An API to set the filtering of functions Steven Rostedt
2021-03-30  0:51 ` [PATCH 02/13 v2] libtracefs: Document function_filter API Steven Rostedt
2021-03-30  0:51 ` [PATCH 03/13 v2] libtracefs: Fix notations of tracefs_function_filter() and module parameter Steven Rostedt
2021-03-30  0:51 ` [PATCH 04/13 v2] libtracefs: Move opening of file out of controlled_write() Steven Rostedt
2021-03-30  0:51 ` [PATCH 05/13 v2] libtracefs: Add add_errors() helper function for control_write() Steven Rostedt
2021-03-30  0:51 ` [PATCH 06/13 v2] libtracefs: Add checking of available_filter_functions to tracefs_function_filter() Steven Rostedt
2021-03-30  0:51 ` [PATCH 07/13 v2] libtracefs: Add write_filter() helper function Steven Rostedt
2021-03-30  0:51 ` [PATCH 08/13 v2] libtracefs: Allow for setting filters with regex expressions Steven Rostedt
2021-04-01 16:33   ` sameeruddin shaik
2021-03-31 16:39     ` Steven Rostedt
2021-04-02  1:59       ` sameeruddin shaik
2021-04-01  2:41         ` Steven Rostedt [this message]
2021-03-30  0:51 ` [PATCH 09/13 v2] libtracefs: Add indexing to set functions in tracefs_function_filter() Steven Rostedt
2021-03-30  0:51 ` [PATCH 10/13 v2] libtracefs: Pass in reset via flags to tracefs_function_filter() Steven Rostedt
2021-03-30 14:29   ` Tzvetomir Stoyanov
2021-03-30 14:53     ` Steven Rostedt
2021-03-30  0:51 ` [PATCH 11/13 v2] libtracefs: Add pthread_mutex_lock() around tracefs_function_filter() Steven Rostedt
2021-03-30  0:51 ` [PATCH 12/13 v2] libtracefs: Move struct tracefs_instance to tracefs-local.h Steven Rostedt
2021-03-30  0:51 ` [PATCH 13/13 v2] libtracefs: Add CONTINUE to tracefs_function_filter() Steven Rostedt
2021-03-30 14:29   ` Tzvetomir Stoyanov
2021-03-30 14:52     ` Steven Rostedt
2021-03-30 15:14       ` Steven Rostedt
2021-03-30 15:32       ` Tzvetomir Stoyanov
2021-03-30 16:03         ` Steven Rostedt
2021-03-30  1:03 ` [RFC][PATCH 14/13 v2] libtracefs: Just past one filter in for tracefs_function_filter() Steven Rostedt
2021-03-30 14:31   ` Tzvetomir Stoyanov

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