From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753992AbbKRGzP (ORCPT ); Wed, 18 Nov 2015 01:55:15 -0500 Received: from mail-wm0-f44.google.com ([74.125.82.44]:33917 "EHLO mail-wm0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751837AbbKRGzN (ORCPT ); Wed, 18 Nov 2015 01:55:13 -0500 Date: Wed, 18 Nov 2015 07:55:08 +0100 From: Ingo Molnar To: "Jason A. Donenfeld" Cc: tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, LKML Subject: Re: irq_fpu_usable() is irreliable Message-ID: <20151118065508.GA18849@gmail.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Jason A. Donenfeld wrote: > [...] Recently I've been tracking down a problem in which irq_fpu_usable() > returns false, yet a stack trace shows the first function is the syscall entry > point. [...] Is this 'problem' a performance problem (code not being able to use the FPU occasionally and hence sporadically performing poorly), or some sort of actual stability/correctness problem? Also, what CPU does the test system have, Intel or AMD? The FPU behavior can be very different in the two cases. Third, could you post such a problematic stack trace? Thanks, Ingo