Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933117AbaFJUbt (ORCPT ); Tue, 10 Jun 2014 16:31:49 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:35004 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753715AbaFJTrN (ORCPT ); Tue, 10 Jun 2014 15:47:13 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Dave Jiang , Ed Ciechanowski , Dan Williams , Tejun Heo , Kamal Mostafa Subject: [PATCH 3.13 072/160] libata/ahci: accommodate tag ordered controllers Date: Tue, 10 Jun 2014 12:45:12 -0700 Message-Id: <1402429600-20477-73-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1402429600-20477-1-git-send-email-kamal@canonical.com> References: <1402429600-20477-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.13 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.13.11.3 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Dan Williams commit 8a4aeec8d2d6a3edeffbdfae451cdf05cbf0fefd upstream. The AHCI spec allows implementations to issue commands in tag order rather than FIFO order: 5.3.2.12 P:SelectCmd HBA sets pSlotLoc = (pSlotLoc + 1) mod (CAP.NCS + 1) or HBA selects the command to issue that has had the PxCI bit set to '1' longer than any other command pending to be issued. The result is that commands posted sequentially (time-wise) may play out of sequence when issued by hardware. This behavior has likely been hidden by drives that arrange for commands to complete in issue order. However, it appears recent drives (two from different vendors that we have found so far) inflict out-of-order completions as a matter of course. So, we need to take care to maintain ordered submission, otherwise we risk triggering a drive to fall out of sequential-io automation and back to random-io processing, which incurs large latency and degrades throughput. This issue was found in simple benchmarks where QD=2 seq-write performance was 30-50% *greater* than QD=32 seq-write performance. Tagging for -stable and making the change globally since it has a low risk-to-reward ratio. Also, word is that recent versions of an unnamed OS also does it this way now. So, drives in the field are already experienced with this tag ordering scheme. Cc: Dave Jiang Cc: Ed Ciechanowski Reviewed-by: Matthew Wilcox Signed-off-by: Dan Williams Signed-off-by: Tejun Heo Signed-off-by: Kamal Mostafa --- drivers/ata/libata-core.c | 21 +++++++++++++-------- include/linux/libata.h | 1 + 2 files changed, 14 insertions(+), 8 deletions(-) diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c index 2897dbe..0a79c54 100644 --- a/drivers/ata/libata-core.c +++ b/drivers/ata/libata-core.c @@ -4794,21 +4794,26 @@ void swap_buf_le16(u16 *buf, unsigned int buf_words) static struct ata_queued_cmd *ata_qc_new(struct ata_port *ap) { struct ata_queued_cmd *qc = NULL; - unsigned int i; + unsigned int i, tag; /* no command while frozen */ if (unlikely(ap->pflags & ATA_PFLAG_FROZEN)) return NULL; - /* the last tag is reserved for internal command. */ - for (i = 0; i < ATA_MAX_QUEUE - 1; i++) - if (!test_and_set_bit(i, &ap->qc_allocated)) { - qc = __ata_qc_from_tag(ap, i); + for (i = 0; i < ATA_MAX_QUEUE; i++) { + tag = (i + ap->last_tag + 1) % ATA_MAX_QUEUE; + + /* the last tag is reserved for internal command. */ + if (tag == ATA_TAG_INTERNAL) + continue; + + if (!test_and_set_bit(tag, &ap->qc_allocated)) { + qc = __ata_qc_from_tag(ap, tag); + qc->tag = tag; + ap->last_tag = tag; break; } - - if (qc) - qc->tag = i; + } return qc; } diff --git a/include/linux/libata.h b/include/linux/libata.h index bec6dbe..3fee55e 100644 --- a/include/linux/libata.h +++ b/include/linux/libata.h @@ -822,6 +822,7 @@ struct ata_port { unsigned long qc_allocated; unsigned int qc_active; int nr_active_links; /* #links with active qcs */ + unsigned int last_tag; /* track next tag hw expects */ struct ata_link link; /* host default link */ struct ata_link *slave_link; /* see ata_slave_link_init() */ -- 1.9.1 -- 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/