Clarifies the RAM footprint of buffer_size_kb without getting into
implementation details.
Changes in v2:
- Removes implementation description of the RAM footprint of
buffer_size_kb, but still make the corresponded clarification.
- Removes a patch that was just for illustration purposes because
Steven already got the issue that I was referring to.
- Adds a patch to fix other typos in the doc.
Frank A. Cancio Bello (2):
docs: ftrace: Clarify the RAM impact of buffer_size_kb
docs: ftrace: Fix typos
Documentation/trace/ftrace.rst | 9 +++++----
Documentation/trace/ring-buffer-design.txt | 2 +-
2 files changed, 6 insertions(+), 5 deletions(-)
--
2.17.1
The current text could mislead the user into believing that the number
of pages allocated by each CPU ring buffer is calculated by the round
up of the division: buffer_size_kb / PAGE_SIZE.
Clarifies that a few extra pages may be allocated to accommodate buffer
management meta-data.
Suggested-by: Steven Rostedt (VMware) <[email protected]>
Suggested-by: Joel Fernandes (Google) <[email protected]>
Signed-off-by: Frank A. Cancio Bello <[email protected]>
---
Documentation/trace/ftrace.rst | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index d2b5657ed33e..2b21068ebf8e 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -185,7 +185,8 @@ of ftrace. Here is a list of some of the key files:
CPU buffer and not total size of all buffers. The
trace buffers are allocated in pages (blocks of memory
that the kernel uses for allocation, usually 4 KB in size).
- If the last page allocated has room for more bytes
+ A few extra pages may be allocated to accommodate buffer management
+ meta-data. If the last page allocated has room for more bytes
than requested, the rest of the page will be used,
making the actual allocation bigger than requested or shown.
( Note, the size may not be a multiple of the page size
--
2.17.1
Fix minor typos in the doc.
Signed-off-by: Frank A. Cancio Bello <[email protected]>
---
Documentation/trace/ftrace.rst | 6 +++---
Documentation/trace/ring-buffer-design.txt | 2 +-
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 2b21068ebf8e..9e7b45485ea1 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -236,7 +236,7 @@ of ftrace. Here is a list of some of the key files:
This interface also allows for commands to be used. See the
"Filter commands" section for more details.
- As a speed up, since processing strings can't be quite expensive
+ As a speed up, since processing strings can be quite expensive
and requires a check of all functions registered to tracing, instead
an index can be written into this file. A number (starting with "1")
written will instead select the same corresponding at the line position
@@ -383,7 +383,7 @@ of ftrace. Here is a list of some of the key files:
By default, 128 comms are saved (see "saved_cmdlines" above). To
increase or decrease the amount of comms that are cached, echo
- in a the number of comms to cache, into this file.
+ in the number of comms to cache, into this file.
saved_tgids:
@@ -3325,7 +3325,7 @@ directories after it is created.
As you can see, the new directory looks similar to the tracing directory
itself. In fact, it is very similar, except that the buffer and
-events are agnostic from the main director, or from any other
+events are agnostic from the main directory, or from any other
instances that are created.
The files in the new directory work just like the files with the
diff --git a/Documentation/trace/ring-buffer-design.txt b/Documentation/trace/ring-buffer-design.txt
index ff747b6fa39b..2d53c6f25b91 100644
--- a/Documentation/trace/ring-buffer-design.txt
+++ b/Documentation/trace/ring-buffer-design.txt
@@ -37,7 +37,7 @@ commit_page - a pointer to the page with the last finished non-nested write.
cmpxchg - hardware-assisted atomic transaction that performs the following:
- A = B iff previous A == C
+ A = B if previous A == C
R = cmpxchg(A, C, B) is saying that we replace A with B if and only if
current A is equal to C, and we put the old (current) A into R
--
2.17.1
On Sun, 24 Nov 2019 23:38:41 -0500
"Frank A. Cancio Bello" <[email protected]> wrote:
> --- a/Documentation/trace/ring-buffer-design.txt
> +++ b/Documentation/trace/ring-buffer-design.txt
> @@ -37,7 +37,7 @@ commit_page - a pointer to the page with the last finished non-nested write.
>
> cmpxchg - hardware-assisted atomic transaction that performs the following:
>
> - A = B iff previous A == C
> + A = B if previous A == C
This wasn't a typo. "iff" means "if and only if" which is a standard
notation. That is, this is shorthand for:
A = B if previous A == C
previous A == C if A = B
-- Steve
>
> R = cmpxchg(A, C, B) is saying that we replace A with B if and only if
> current A is equal to C, and we put the old (current) A into R
> --
On Mon, 25 Nov 2019 12:37:09 -0500
Steven Rostedt <[email protected]> wrote:
> On Sun, 24 Nov 2019 23:38:41 -0500
> "Frank A. Cancio Bello" <[email protected]> wrote:
>
> > --- a/Documentation/trace/ring-buffer-design.txt
> > +++ b/Documentation/trace/ring-buffer-design.txt
> > @@ -37,7 +37,7 @@ commit_page - a pointer to the page with the last finished non-nested write.
> >
> > cmpxchg - hardware-assisted atomic transaction that performs the following:
> >
> > - A = B iff previous A == C
> > + A = B if previous A == C
>
> This wasn't a typo. "iff" means "if and only if" which is a standard
> notation. That is, this is shorthand for:
>
> A = B if previous A == C
> previous A == C if A = B
Although thinking about this more, this may not be correct. If
previous A == B, then A = B, thus the "iff" notation is not actually
accurate.
This wouldn't then be a typo fix, but a real fix to the logic ;-)
-- Steve
>
>
> >
> > R = cmpxchg(A, C, B) is saying that we replace A with B if and only if
> > current A is equal to C, and we put the old (current) A into R
> > --
On Mon, Nov 25, 2019 at 04:46:25PM -0500, Steven Rostedt wrote:
> On Mon, 25 Nov 2019 12:37:09 -0500
> Steven Rostedt <[email protected]> wrote:
>
> > On Sun, 24 Nov 2019 23:38:41 -0500
> > "Frank A. Cancio Bello" <[email protected]> wrote:
> >
> > > --- a/Documentation/trace/ring-buffer-design.txt
> > > +++ b/Documentation/trace/ring-buffer-design.txt
> > > @@ -37,7 +37,7 @@ commit_page - a pointer to the page with the last finished non-nested write.
> > >
> > > cmpxchg - hardware-assisted atomic transaction that performs the following:
> > >
> > > - A = B iff previous A == C
> > > + A = B if previous A == C
> >
> > This wasn't a typo. "iff" means "if and only if" which is a standard
> > notation. That is, this is shorthand for:
> >
> > A = B if previous A == C
> > previous A == C if A = B
>
> Although thinking about this more, this may not be correct. If
> previous A == B, then A = B, thus the "iff" notation is not actually
> accurate.
>
> This wouldn't then be a typo fix, but a real fix to the logic ;-)
>
What are the odds ;)
I knew about the concept https://en.wikipedia.org/wiki/If_and_only_if
from school math but didn't remember the notation. For me was
suspicious so, I looked in "the cmpxchg doc" and nothing referring
to "iff" was there, then I decided to classified it as a typo.
Now thinking more deeply, I agreed with you that was not a typo but
a "logic mistake", even not for the same reason ;)
Being not 100% sure of what I'm about to say, I will say it
anyway because you have been kind enough to write the second email.
"if and only if (shortened as iff) is a biconditional logical
connective between statements" and A = B can't be considered a
logical statement in the context of that definition (math/logic),
even it could be in C.
Thank you Steven one more time for such a quick reply!
frank a.