Re: [PATCH v6 0/8] Additional kmsg devices

From: Tejun Heo
Date: Thu Feb 25 2016 - 16:47:21 EST

Hello, Kazimierz.

On Wed, Feb 24, 2016 at 12:53:13PM +0100, Kazimierz Krosman wrote:
> 1. kmsg device does not require maintenance by reader process side.
> Multiple writers can write to a device and new records overwrite logs saved earlier.
> When system crashes logs can be restored with pstore mechanism.

I'm not sure this is the right layer to implement generic logging

> 2. Using kmsg can cause lower CPU utilisation in the real-word use case than
> userspace logging mechanisms.
> We created 2 tests: (1) 100 writer processes write to created kmsg buffer and
> (2) 100 writers write to socket (stream)- there is one reader to protect
> socket buffer against overflow. Tests show that cpu utilisation in case of first
> test is about 2.3 times lower (39.1%) than it is in second case (87.7%) (measured
> with top program; tests code is attached below). Tested on Odroid XU4.

This sounds like a generic IPC problem than anything else.