From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Cox Subject: [RESEND RFC PATCH] libata: cache device select Date: Wed, 05 May 2010 10:27:47 +0100 Message-ID: <20100505092730.960.94960.stgit@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:39746 "EHLO bob.linux.org.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932398Ab0EEKGQ (ORCPT ); Wed, 5 May 2010 06:06:16 -0400 Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: jeff@garzik.org, linux-ide@vger.kernel.org Avoid the device select overhead on every qc_issue (> 10uS) by caching the currently selected device. This shows up on profiles under load. Signed-off-by: Alan Cox --- drivers/ata/libata-sff.c | 6 +++++- include/linux/libata.h | 1 + 2 files changed, 6 insertions(+), 1 deletions(-) diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c index 4b57ae9..4fb1229 100644 --- a/drivers/ata/libata-sff.c +++ b/drivers/ata/libata-sff.c @@ -470,6 +470,7 @@ void ata_sff_dev_select(struct ata_port *ap, unsigned int device) iowrite8(tmp, ap->ioaddr.device_addr); ata_sff_pause(ap); /* needed; also flushes, for mmio */ + ap->sff_selected = device; } EXPORT_SYMBOL_GPL(ata_sff_dev_select); @@ -1559,7 +1560,8 @@ unsigned int ata_sff_qc_issue(struct ata_queued_cmd *qc) } /* select the device */ - ata_dev_select(ap, qc->dev->devno, 1, 0); + if (qc->dev->devno != ap->sff_selected) + ata_dev_select(ap, qc->dev->devno, 1, 0); /* start the command */ switch (qc->tf.protocol) { @@ -1971,6 +1973,8 @@ int ata_sff_prereset(struct ata_link *link, unsigned long deadline) struct ata_eh_context *ehc = &link->eh_context; int rc; + link->ap->sff_selected = -1; /* Unknown */ + rc = ata_std_prereset(link, deadline); if (rc) return rc; diff --git a/include/linux/libata.h b/include/linux/libata.h index c4811d9..63a9489 100644 --- a/include/linux/libata.h +++ b/include/linux/libata.h @@ -727,6 +727,7 @@ struct ata_port { #ifdef CONFIG_ATA_SFF struct ata_ioports ioaddr; /* ATA cmd/ctl/dma register blocks */ + int sff_selected; /* Cache of selected device */ #endif /* CONFIG_ATA_SFF */ u8 ctl; /* cache of ATA control register */