Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755298AbbBTTGv (ORCPT ); Fri, 20 Feb 2015 14:06:51 -0500 Received: from mail.skyhub.de ([78.46.96.112]:41828 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752324AbbBTTGu (ORCPT ); Fri, 20 Feb 2015 14:06:50 -0500 Date: Fri, 20 Feb 2015 20:05:54 +0100 From: Borislav Petkov To: Andy Lutomirski Cc: Oleg Nesterov , Rik van Riel , x86@kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds Subject: Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs Message-ID: <20150220190554.GJ19378@pd.tnic> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 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 Content-Length: 1964 Lines: 58 + Linus. I'm sure he'll save something to say about it :-) On Fri, Feb 20, 2015 at 10:58:15AM -0800, Andy Lutomirski wrote: > We have eager and lazy fpu modes, introduced in: > > 304bceda6a18 x86, fpu: use non-lazy fpu restore for processors supporting xsave > > The result is rather messy. There are two code paths in almost all of the > FPU code, and only one of them (the eager case) is tested frequently, since > most kernel developers have new enough hardware that we use eagerfpu. > > It seems that, on any remotely recent hardware, eagerfpu is a win: > glibc uses SSE2, so laziness is probably overoptimistic, and, in any > case, manipulating TS is far slower that saving and restoring the full > state. > > To try to shake out any latent issues on old hardware, this changes > the default to eager on all CPUs. If no performance or functionality > problems show up, a subsequent patch could remove lazy mode entirely. > > Signed-off-by: Andy Lutomirski > --- > arch/x86/kernel/xsave.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c > index 0de1fae2bdf0..1928c8f34ce5 100644 > --- a/arch/x86/kernel/xsave.c > +++ b/arch/x86/kernel/xsave.c > @@ -637,8 +637,8 @@ static void __init xstate_enable_boot_cpu(void) > prepare_fx_sw_frame(); > setup_init_fpu_buf(); > > - /* Auto enable eagerfpu for xsaveopt */ > - if (cpu_has_xsaveopt && eagerfpu != DISABLE) > + /* Auto enable eagerfpu for everyone */ > + if (eagerfpu != DISABLE) > eagerfpu = ENABLE; > > if (pcntxt_mask & XSTATE_EAGER) { > -- > 2.1.0 > > -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/