linux-mips
[Top] [All Lists]

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

To: Jon Mason <jon.mason@intel.com>
Subject: Re: [PATCH RFC 54/77] ntb: Ensure number of MSIs on SNB is enough for the link interrupt
From: Alexander Gordeev <agordeev@redhat.com>
Date: Mon, 7 Oct 2013 20:38:45 +0200
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
In-reply-to: <20131007165056.GA24536@jonmason-lab>
List-archive: <http://www.linux-mips.org/archives/linux-mips/>
List-help: <mailto:ecartis@linux-mips.org?Subject=help>
List-id: linux-mips <linux-mips.eddie.linux-mips.org>
List-owner: <mailto:ralf@linux-mips.org>
List-post: <mailto:linux-mips@linux-mips.org>
List-software: Ecartis version 1.0.0
List-subscribe: <mailto:ecartis@linux-mips.org?subject=subscribe%20linux-mips>
List-unsubscribe: <mailto:ecartis@linux-mips.org?subject=unsubscribe%20linux-mips>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <cover.1380703262.git.agordeev@redhat.com> <5d9c5b2d3bbc444ff32bddeece7a239d046bd79c.1380703263.git.agordeev@redhat.com> <20131003004805.GL6768@jonmason-lab> <20131005214303.GA21589@dhcp-26-207.brq.redhat.com> <20131007165056.GA24536@jonmason-lab>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Oct 07, 2013 at 09:50:57AM -0700, Jon Mason wrote:
> 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.

The changelog is definitely bogus. I meant here an improvement to the
existing scheme, not a conversion to the new one:

        msix_entries = msix_table_size(val);

Getting i.e. 16 vectors here.

        if (msix_entries > ndev->limits.msix_cnt) {
                rc = -EINVAL;
                goto err;
        }

Upper limit check i.e. succeeds.

        [...]

        rc = pci_enable_msix(pdev, ndev->msix_entries, msix_entries);

pci_enable_msix() does not success and returns i.e. 8 here, should retry.

        if (rc < 0)
                goto err1;
        if (rc > 0) {
                /* 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) {

On SNB bail out here, although could have continue with 8 vectors.
Can only use SNB_MSIX_CNT here, since limits.msix_cnt is the upper limit.

                        rc = -EIO;
                        goto err1;
                }

                [...]
        }

-- 
Regards,
Alexander Gordeev
agordeev@redhat.com

<Prev in Thread] Current Thread [Next in Thread>