[lkml]   [2018]   [Jul]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: ftrace global trace_pipe_raw
Hello Steve,

thank you for your answer,

On 07/24/2018 04:25 PM, Steven Rostedt wrote:
> On Tue, 24 Jul 2018 10:23:16 -0400
> Steven Rostedt <> wrote:
>>> Would work in the direction of adding a global trace_pipe_raw be considered
>>> for inclusion?
>> The design of the lockless ring buffer requires not to be preempted,
>> and that the data cannot be written to from more than one location. To
>> do so, we make a per CPU buffer, and disable preemption when writing.
>> This means that we have only one writer at a time. It can handle
>> interrupts and NMIs, because they will finish before they return and
>> this doesn't break the algorithm. But having writers from multiple CPUs
>> would require locking or other heaving synchronization operations that
>> will greatly reduce the speed of writing to the buffers (not to mention
>> the cache thrashing).

I understand, it is not a simple matter then.

> And why would you need a single buffer?

I am interested in all events that have to do with a specific task,
regardless of the CPU they appear on.
Having an already post-processed stream of binary data would be awesome I think.

> Note, we are working on making
> that will allow applications to read the buffers and the
> library will take care of the interleaving of the raw data. This should
> hopefully be ready in about three months or so.
> -- Steve

That would be great! So the library could handle this kind of preprocessing,
and create a single stream of sorted timestamps/events with the binary data?

Thanks a lot,


 \ /
  Last update: 2018-07-24 17:31    [W:0.096 / U:1.232 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site