From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: [PATCHSET] prep for PMP support, take 3 Date: Tue, 31 Oct 2006 21:22:03 -0500 Message-ID: <454804CB.9030805@pobox.com> References: <11609542672061-git-send-email-htejun@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:32470 "EHLO mail.dvmed.net") by vger.kernel.org with ESMTP id S1946023AbWKACWJ (ORCPT ); Tue, 31 Oct 2006 21:22:09 -0500 In-Reply-To: <11609542672061-git-send-email-htejun@gmail.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Tejun Heo Cc: alan@lxorguk.ukuu.org.uk, linux-ide@vger.kernel.org Tejun Heo wrote: > Hello, all. > > This is the third take of libata-pmp-prep patchset. This patchset > contains 5 patches and implements various stuff needed for PMP. > > Changes from the last take[L] are. > > * rebased > * sata_link_hardreset() separation is done earlier by vt8251-ahci > patchset and thus dropped from this patchset. > > This patchset is against > > upstream (da54f5fe54c7d75e2db7d17961fb36a8c28a8501) > + [1] hp-poll patchset, take #5 > + [2] vt8251-ahci patchset, take #2 > + [3] libata-link patchset, take #3 > > Git tree can be accessed at > > http://htj.dyndns.org/git/?p=libata-tj.git;a=shortlog;h=pmp-prep > git://htj.dyndns.org/libata-tj pmp-prep > > Jeff, I couldn't merge ->qc_defer() into ->qc_prep() or ->qc_issue(). > The problem is that ->qc_prep() is done after sg mapping is done which > is a bit costly to throw away if the qc has to be deferred. > ->qc_defer() is called right after qc is allocated and translated but > before any resource for qc execution is acuquired. > > Another way would be to let ->qc_issue() determine whether deferring > is needed and cache prepared qc while deferred. This has the > following problems. > > * qc and related resources are held by deferred command. Currently, > qc directly maps to hardware command slots and w/ PMP this can get > messy. > > * Separate requeueing/restarting mechanism must be implemented. ATM, > libata depends on SCSI for retrying deferred commands with > reasonable fairness. To hold prepared qc, libata needs to implement > its own mechanism and I don't think the added benefits justify the > complexity. > > So, I think it's better to keep ->qc_defer(). Weak ACK for the patchset: SET FEATURES - XFER MODE also needs to use the defer capability. And we also have such a need for simplex devices. It would be useful to have all of this stuff collected into an "ATA command scheduling / sequencing" area, rather than just a new hook confined to a single area. I think the problem space is more complex than that. Jeff