From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758328Ab2HUSMU (ORCPT ); Tue, 21 Aug 2012 14:12:20 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:14643 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754161Ab2HUSMQ (ORCPT ); Tue, 21 Aug 2012 14:12:16 -0400 X-Authority-Analysis: v=2.0 cv=Vb91zSV9 c=1 sm=0 a=rXTBtCOcEpjy1lPqhTCpEQ==:17 a=mNMOxpOpBa8A:10 a=qkHp1cYU9ngA:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=A_osGyS-vk0A:10 a=meVymXHHAAAA:8 a=KNaezN3EGSPTaKAtNlcA:9 a=PUjeQqilurYA:10 a=rXTBtCOcEpjy1lPqhTCpEQ==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.115.198 Message-ID: <1345572733.5069.9.camel@gandalf.local.home> Subject: Re: Using random in interrupts for RT From: Steven Rostedt To: Thomas Gleixner Cc: LKML , Ben Hutchings , RT , Theodore Tso Date: Tue, 21 Aug 2012 14:12:13 -0400 In-Reply-To: <1344954649.6724.13.camel@gandalf.stny.rr.com> References: <1344954649.6724.13.camel@gandalf.stny.rr.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.4.3-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2012-08-14 at 10:30 -0400, Steven Rostedt wrote: > Thomas, > > Ben Hutchings asked me if we still need "genirq: Disable random call on > preempt-rt" for -rt? With commit 902c098a366 "random: use lockless > techniques in the interrupt path" there is no more locks used. But does > it still produce high latencies? Ben, Looks that the #ifndef can't be removed just yet. The code is not totally lockless... add_interrupt_randomness -> credit_entropy_bits -> kill_fasync -> kill_fasync_rcu -> spin_lock_irqsave(&fa->fa_lock, flags) to make things worse, that spinlock turns into a mutex on -rt, so it may crash the box if triggered. -- Steve