linux-kernel - Re: [PATCH v3 6/5] AHCI: Do not read HOST_IRQ

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Date:	Fri, 19 Sep 2014 09:34:34 -0700
From:	Dan Williams <dan.j.williams@...il.com>
To:	Alexander Gordeev <agordeev@...hat.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"IDE/ATA development list" <linux-ide@...r.kernel.org>,
	"Jiang, Dave" <dave.jiang@...el.com>
Subject: Re: [PATCH v3 6/5] AHCI: Do not read HOST_IRQ_STAT register in
 multi-MSI mode

On Fri, Sep 19, 2014 at 1:25 AM, Alexander Gordeev <agordeev@...hat.com> wrote:
> As described in AHCI v1.0 specification chapter 10.6.2.2
> "Multiple MSI Based Messages" generation of interrupts
> is not controlled through the HOST_IRQ_STAT register.
>
> Considering MMIO access is expensive remove unnecessary
> reading and writing of HOST_IRQ_STAT register.
>
> Further, serializing access to the host data is no longer
> needed and the interrupt service routine can avoid competing
> on the host lock.
>
> Signed-off-by: Alexander Gordeev <agordeev@...hat.com>
> Suggested-by: "Jiang, Dave" <dave.jiang@...el.com>
> Cc: linux-ide@...r.kernel.org
> ---
>  drivers/ata/ahci.h    |  1 +
>  drivers/ata/libahci.c | 54 ++++++++-------------------------------------------
>  2 files changed, 9 insertions(+), 46 deletions(-)
>
> diff --git a/drivers/ata/ahci.h b/drivers/ata/ahci.h
> index c12f590..b8e117a 100644
> --- a/drivers/ata/ahci.h
> +++ b/drivers/ata/ahci.h
> @@ -305,6 +305,7 @@ struct ahci_port_priv {
>         unsigned int            ncq_saw_dmas:1;
>         unsigned int            ncq_saw_sdb:1;
>         u32                     intr_status;    /* interrupts to handle */
> +       spinlock_t              intr_lock;      /* protects intr_status */

Why introduce a new lock?  Can't we switch to per-ata port locking
rather than ata_host locking?
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