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

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Date:	Thu, 25 Feb 2016 16:47:14 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Kazimierz Krosman <k.krosman@...sung.com>
Cc:	akpm@...ux-foundation.org, peter@...leysoftware.com,
	vvs@...tuozzo.com, corbet@....net, arnd@...db.de, pmladek@...e.cz,
	gregkh@...uxfoundation.org, daniel@...que.org,
	kay.sievers@...y.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-api@...r.kernel.org,
	k.lewandowsk@...sung.com, m.niesluchow@...sung.com,
	richard.weinberger@...il.com, b.zolnierkie@...sung.com,
	luto@...capital.net, knhoon.baik@...sung.com
Subject: Re: [PATCH v6 0/8] Additional kmsg devices

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
facility.

> 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.

Thanks.

-- 
tejun