From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: ahci: CAP_SSS and parallel scan Date: Sat, 08 May 2010 17:53:30 -0400 Message-ID: <4BE5DD5A.8030701@garzik.org> References: <4BE27C49.5090809@kernel.org> <4BE28C4F.9000903@linux.intel.com> <4BE2D5D6.1010705@kernel.org> <4BE31D57.6020400@garzik.org> <4BE3A1A6.1040106@kernel.org> <4BE48742.8060604@garzik.org> <4BE52383.9080908@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-vw0-f46.google.com ([209.85.212.46]:55642 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753625Ab0EHVxd (ORCPT ); Sat, 8 May 2010 17:53:33 -0400 Received: by vws3 with SMTP id 3so625441vws.19 for ; Sat, 08 May 2010 14:53:33 -0700 (PDT) In-Reply-To: <4BE52383.9080908@kernel.org> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Tejun Heo Cc: Arjan van de Ven , t.artem@mailcity.com, "linux-ide@vger.kernel.org" On 05/08/2010 04:40 AM, Tejun Heo wrote: > On 05/07/2010 11:33 PM, Jeff Garzik wrote: >> I'm not sure the usefulness is limited, as it definitely avoids power >> spikes on server BIOSen that care. > > So, are there actually machines which get affected by this? In that > case, sure, the current behavior is the right one. The current behavior is the safe, conservative interpretation. The alternative is risking unwanted power spikes for the sake of boot speed. I would set a high barrier for taking that risk: polling multiple hardware vendors about in-the-field SSS usage. >> Also, it seems unwise for the Linux SATA driver to do the exact >> -opposite- of what the SSS bit intends, by default. > > Yeah, well, the thing is that SSS in itself doesn't really indicate > need for staggered spin up. It just says it knows how to. A valid point, I agree. But absent any other method of communicating that SSS behavior is desired, activating staggered spin-up based on SSS is the only logical interpretation, AFAICS. SSS bit set implies SSS -might- be needed. If SSS might be needed, then one must stagger spin-up or risk failing to meet the requirement. !SSS is the only case where you are -guaranteed- not to need staggered spin-up. Jeff