Re: [RFC PATCH 0/5] Introduce /proc/all/ to gather stats from all processes

On Wed, Aug 12, 2020 at 10:47:32PM -0600, David Ahern wrote:

On 8/12/20 1:51 AM, Andrei Vagin wrote:

quoted

I rebased the task_diag patches on top of v5.8:
https://github.com/avagin/linux-task-diag/tree/v5.8-task-diag

Thanks for updating the patches.

quoted

/proc/pid files have three major limitations:
* Requires at least three syscalls per process per file
  open(), read(), close()
* Variety of formats, mostly text based
  The kernel spent time to encode binary data into a text format and
  then tools like top and ps spent time to decode them back to a binary
  format.
* Sometimes slow due to extra attributes
  For example, /proc/PID/smaps contains a lot of useful informations
  about memory mappings and memory consumption for each of them. But
  even if we don't need memory consumption fields, the kernel will
  spend time to collect this information.

that's what I recall as well.

quoted

More details and numbers are in this article:
https://avagin.github.io/how-fast-is-procfs

This new interface doesn't have only one of these limitations, but
task_diag doesn't have all of them.

And I compared how fast each of these interfaces:

The test environment:
CPU: Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz
RAM: 16GB
kernel: v5.8 with task_diag and /proc/all patches.
100K processes:
$ ps ax | wc -l
10228

100k processes but showing 10k here??

I'm sure that one zero has been escaped from here. task_proc_all shows
a number of tasks too and it shows 100230.

quoted

$ time cat /proc/all/status > /dev/null

real	0m0.577s
user	0m0.017s
sys	0m0.559s

task_proc_all is used to read /proc/pid/status for all tasks:
https://github.com/avagin/linux-task-diag/blob/master/tools/testing/selftests/task_diag/task_proc_all.c

$ time ./task_proc_all status
tasks: 100230

Thanks,
Andrei