From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: ahci: CAP_SSS and parallel scan Date: Thu, 06 May 2010 15:49:43 -0400 Message-ID: <4BE31D57.6020400@garzik.org> References: <4BE27C49.5090809@kernel.org> <4BE28C4F.9000903@linux.intel.com> <4BE2D5D6.1010705@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]:50111 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757122Ab0EFTtr (ORCPT ); Thu, 6 May 2010 15:49:47 -0400 Received: by vws18 with SMTP id 18so106075vws.19 for ; Thu, 06 May 2010 12:49:45 -0700 (PDT) In-Reply-To: <4BE2D5D6.1010705@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 05/06/2010 10:44 AM, Tejun Heo wrote: > Hello, > > On 05/06/2010 11:30 AM, Arjan van de Ven wrote: >> The thing is, SSS means the system requests (well, demands) that we >> don't spin up the disks up in parallel.... which we really really >> ought to honor... Jeff had a very valid point. > > Hmmm... yeah but SSS doesn't really demand it. It just says "I can do > staggered spin up". I wish this thing had been implemented in the > form of "stay spin down till necessary (ie. start in standby mode)". > Currently, there's no way to tell whether staggered spin up is needed > or drives are already spun up. > >> While today some bioses may spin everything up, that's not going to >> be the case going forward... the industry as a whole is moving away >> from that (slowly but steadily). > > Yeah, sure, in the long run maybe but I'm skeptical how useful this is > at this point. Going forward, the right thing to do would be > implementing some sort of token infrastructure so that drivers can > request and hold the token while spinning up a drive so that the > concurrency of spin ups can be controlled. > > Jeff, what do you think about lifting the check for now unless there > are known cases where this can cause problems? The problem being... that we are honoring SSS bit, and thus thing are slower? :) I don't see any reason to change that, seeing as how people may be using it to avoid power spikes. I agree there's no way to tell whether SSS is needed, but we cannot ignore SSS on that basis alone. We should avoid making the assumption that BIOS w/ SSS bit has already spun up all drives regardless. Jeff