linux-kernel - Re: [PATCH v2 -tip 5/5] AHCI: Support multiple MSIs

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Message-ID: <5063DD23.5050504@pobox.com>
Date:	Thu, 27 Sep 2012 00:59:15 -0400
From:	Jeff Garzik <jgarzik@...ox.com>
To:	Alexander Gordeev <agordeev@...hat.com>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Matthew Wilcox <willy@...ux.intel.com>, x86@...nel.org,
	linux-pci@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: [PATCH v2 -tip 5/5] AHCI: Support multiple MSIs

On 09/03/2012 05:20 AM, Alexander Gordeev wrote:
> Take advantage of multiple MSIs implementation on x86 - on systems with
> IRQ remapping AHCI ports not only get assigned separate MSI vectors -
> but also separate IRQs. As result, interrupts generated by different
> ports could be serviced on different CPUs rather than on a single one.
>
> In cases when number of allocated MSIs is less than requested the Sharing
> Last MSI mode does not get used, no matter implemented in hardware or not.
> Instead, the driver assumes the advantage of multiple MSIs is negated and
> falls back to the single MSI mode as if MRSM bit was set (some Intel chips
> implement this strategy anyway - MRSM bit gets set even if the number of
> allocated MSIs exceeds the number of implemented ports).
>
> Signed-off-by: Alexander Gordeev <agordeev@...hat.com>
> ---
>   drivers/ata/ahci.c    |   14 ++--
>   drivers/ata/ahci.h    |    5 +
>   drivers/ata/libahci.c |  211 +++++++++++++++++++++++++++++++++++++++++++++++--
>   3 files changed, 218 insertions(+), 12 deletions(-)

OK, round 2 :)

Reviewed the locking twice, and cannot find any problems there.  That 
was my main concern.

Other problems noted:

1) Including linux/pci.h into libahci.c should have been a hint ;p

libahci is entirely PCI-free, AHCI-specific code.  All code that is 
specific to PCI hosts goes into ahci.c.  Anything in libahci needs to be 
purely iomem read/write, standard AHCI DMA data structure manipulation, 
etc.  This is shared with ahci_platform.

So, move the PCI specific code back into ahci.c.  Thus, 
ahci_hw_interrupt appears like libahci material, but 
ahci_init_interrupts is not.

2) don't manually add new "static inline", let the compiler figure it out

3) spinlock init, such as in e.g. ahci_set_per_port_lock() should occur 
with the rest of ahci_port_priv initialization, inside ahci_port_start()

Otherwise it looks OK and ready for merging, after these updates.




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