netdev - Re: [PATCH RFC 50/77] mlx5: Update MSI/MSI-X interrupts enablement code

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Message-ID: <20131003194837.GA27636@dhcp-26-207.brq.redhat.com>
Date:	Thu, 3 Oct 2013 21:48:39 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Eli Cohen <eli@....mellanox.co.il>
Cc:	linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Michael Ellerman <michael@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Andy King <acking@...are.com>, Jon Mason <jon.mason@...el.com>,
	Matt Porter <mporter@...nel.crashing.org>,
	linux-pci@...r.kernel.org, linux-mips@...ux-mips.org,
	linuxppc-dev@...ts.ozlabs.org, linux390@...ibm.com,
	linux-s390@...r.kernel.org, x86@...nel.org,
	linux-ide@...r.kernel.org, iss_storagedev@...com,
	linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net,
	linux-driver@...gic.com,
	Solarflare linux maintainers <linux-net-drivers@...arflare.com>,
	"VMware, Inc." <pv-drivers@...are.com>, linux-scsi@...r.kernel.org
Subject: Re: [PATCH RFC 50/77] mlx5: Update MSI/MSI-X interrupts enablement
 code

On Thu, Oct 03, 2013 at 10:14:33AM +0300, Eli Cohen wrote:
> On Wed, Oct 02, 2013 at 12:49:06PM +0200, Alexander Gordeev wrote:
> >  
> > +	err = pci_msix_table_size(dev->pdev);
> > +	if (err < 0)
> > +		return err;
> > +
> >  	nvec = dev->caps.num_ports * num_online_cpus() + MLX5_EQ_VEC_COMP_BASE;
> >  	nvec = min_t(int, nvec, num_eqs);
> > +	nvec = min_t(int, nvec, err);
> >  	if (nvec <= MLX5_EQ_VEC_COMP_BASE)
> >  		return -ENOSPC;
> 
> Making sure we don't request more vectors then the device's is capable
> of -- looks good.
> >  
> > @@ -131,20 +136,15 @@ static int mlx5_enable_msix(struct mlx5_core_dev *dev)
> >  	for (i = 0; i < nvec; i++)
> >  		table->msix_arr[i].entry = i;
> >  
> > -retry:
> > -	table->num_comp_vectors = nvec - MLX5_EQ_VEC_COMP_BASE;
> >  	err = pci_enable_msix(dev->pdev, table->msix_arr, nvec);
> > -	if (err <= 0) {
> > +	if (err) {
> > +		kfree(table->msix_arr);
> >  		return err;
> > -	} else if (err > MLX5_EQ_VEC_COMP_BASE) {
> > -		nvec = err;
> > -		goto retry;
> >  	}
> >  
> 
> According to latest sources, pci_enable_msix() may still fail so why
> do you want to remove this code?

pci_enable_msix() may fail, but it can not return a positive number.

We first calculate how many MSI-Xs we need, adjust to what we can get,
check if that is enough and only then go for it.

> > -	mlx5_core_dbg(dev, "received %d MSI vectors out of %d requested\n", err, nvec);
> > -	kfree(table->msix_arr);
> > +	table->num_comp_vectors = nvec - MLX5_EQ_VEC_COMP_BASE;
> >  
> > -	return -ENOSPC;
> > +	return 0;
> >  }
> >  
> >  static void mlx5_disable_msix(struct mlx5_core_dev *dev)

-- 
Regards,
Alexander Gordeev
agordeev@...hat.com
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