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Re: [PATCH RFC 54/77] ntb: Ensure number of MSIs on SNB is enough for th

To: Alexander Gordeev <agordeev@redhat.com>
Subject: Re: [PATCH RFC 54/77] ntb: Ensure number of MSIs on SNB is enough for the link interrupt
From: Jon Mason <jon.mason@intel.com>
Date: Mon, 7 Oct 2013 09:50:57 -0700
Cc: linux-kernel@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>, Ralf Baechle <ralf@linux-mips.org>, Michael Ellerman <michael@ellerman.id.au>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Ingo Molnar <mingo@redhat.com>, Tejun Heo <tj@kernel.org>, Dan Williams <dan.j.williams@intel.com>, Andy King <acking@vmware.com>, Matt Porter <mporter@kernel.crashing.org>, stable@vger.kernel.org, linux-pci@vger.kernel.org, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, linux390@de.ibm.com, linux-s390@vger.kernel.org, x86@kernel.org, linux-ide@vger.kernel.org, iss_storagedev@hp.com, linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, netdev@vger.kernel.org, e1000-devel@lists.sourceforge.net, linux-driver@qlogic.com, Solarflare linux maintainers <linux-net-drivers@solarflare.com>, "VMware, Inc." <pv-drivers@vmware.com>, linux-scsi@vger.kernel.org
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On Sat, Oct 05, 2013 at 11:43:04PM +0200, Alexander Gordeev wrote:
> On Wed, Oct 02, 2013 at 05:48:05PM -0700, Jon Mason wrote:
> > On Wed, Oct 02, 2013 at 12:49:10PM +0200, Alexander Gordeev wrote:
> > > Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
> > > ---
> > >  drivers/ntb/ntb_hw.c |    2 +-
> > >  1 files changed, 1 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/drivers/ntb/ntb_hw.c b/drivers/ntb/ntb_hw.c
> > > index de2062c..eccd5e5 100644
> > > --- a/drivers/ntb/ntb_hw.c
> > > +++ b/drivers/ntb/ntb_hw.c
> > > @@ -1066,7 +1066,7 @@ static int ntb_setup_msix(struct ntb_device *ndev)
> > >           /* On SNB, the link interrupt is always tied to 4th vector.  If
> > >            * we can't get all 4, then we can't use MSI-X.
> > >            */
> > > -         if (ndev->hw_type != BWD_HW) {
> > > +         if ((rc < SNB_MSIX_CNT) && (ndev->hw_type != BWD_HW)) {
> > 
> > Nack, this check is unnecessary.
> 
> If SNB can do more than SNB_MSIX_CNT MSI-Xs then this check is needed
> to enable less than maximum MSI-Xs in case the maximum was not allocated.
> Otherwise SNB will fallback to single MSI instead of multiple MSI-Xs.

Per the comment in the code snippet above, "If we can't get all 4,
then we can't use MSI-X".  There is already a check to see if more
than 4 were acquired.  So it's not possible to hit this.  Even if it
was, don't use SNB_MSIX_CNT here (limits.msix_cnt is the preferred
variable).  Also, the "()" are unnecessary.

Thanks,
Jon

> -- 
> Regards,
> Alexander Gordeev
> agordeev@redhat.com

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