From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stanislav Meduna Subject: Re: loading pages to memory causes high latency Date: Sat, 27 Oct 2012 11:06:26 +0200 Message-ID: <508BA412.5020708@meduna.org> References: <508ACFCF.8040001@meduna.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit To: linux-rt-users@vger.kernel.org Return-path: Received: from www.meduna.org ([92.240.244.38]:44272 "EHLO meduna.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750730Ab2J0JGn (ORCPT ); Sat, 27 Oct 2012 05:06:43 -0400 Received: from dial-95-105-165-4-orange.orange.sk ([95.105.165.4] helo=[192.168.130.22]) by meduna.org with esmtpsa (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.72) (envelope-from ) id 1TS2Lh-0000uH-6J for linux-rt-users@vger.kernel.org; Sat, 27 Oct 2012 11:06:39 +0200 In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: On 27.10.2012 10:38, Thomas Gleixner wrote: > There is not much we can do about that unless we want to do a major > surgery on that pata driver code. > > So either you disable the throttler or you reconfigure the pata irq > thread to SCHED_OTHER, which will slow it down a bit, but avoids the > hogging of the machine with a RT task going wild. Thank you for the analysis. Yep I'll reconfigure it to SCHED_OTHER - file access is a totally low-prio thing in my application and I was more afraid of a possibility where someone fetching logfiles or something like that will bring the application to the knees. BTW what granularity does the throttler have? I cannot live with 50 ms lag once in a second, but in my case I can well live with 5 ms lag once in 100 ms (even if that means that the throttler would be activated more often). Right now I have CONFIG_TICK_ONESHOT=y CONFIG_NO_HZ=y CONFIG_HZ=1000 CONFIG_SCHED_HRTICK=y and lacking better choices my clock source is TSC. I admit that I do not know what precisely each setting does - the NO_HZ combined with HZ=1000 looks a bit weird ;) Best regards -- Stano