From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751447AbcBYVrS (ORCPT ); Thu, 25 Feb 2016 16:47:18 -0500 Received: from mail-yw0-f193.google.com ([209.85.161.193]:34739 "EHLO mail-yw0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750717AbcBYVrQ (ORCPT ); Thu, 25 Feb 2016 16:47:16 -0500 Date: Thu, 25 Feb 2016 16:47:14 -0500 From: Tejun Heo To: Kazimierz Krosman Cc: akpm@linux-foundation.org, peter@hurleysoftware.com, vvs@virtuozzo.com, corbet@lwn.net, arnd@arndb.de, pmladek@suse.cz, gregkh@linuxfoundation.org, daniel@zonque.org, kay.sievers@vrfy.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-api@vger.kernel.org, k.lewandowsk@samsung.com, m.niesluchow@samsung.com, richard.weinberger@gmail.com, b.zolnierkie@samsung.com, luto@amacapital.net, knhoon.baik@samsung.com Subject: Re: [PATCH v6 0/8] Additional kmsg devices Message-ID: <20160225214714.GJ6092@mtj.duckdns.org> References: <1456314801-32738-1-git-send-email-k.krosman@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1456314801-32738-1-git-send-email-k.krosman@samsung.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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