linux-kernel - Re: [PATCH RFC 46/77] mlx4: Update MSI/MSI-X interrupts enablement code

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Message-ID: <20131003110254.5f10fbb8@jpm-OptiPlex-GX620>
Date:	Thu, 3 Oct 2013 11:02:54 +0300
From:	Jack Morgenstein <jackm@....mellanox.co.il>
To:	Alexander Gordeev <agordeev@...hat.com>
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,
	ogerlitz@...lanox.com, eli@...lanox.com
Subject: Re: [PATCH RFC 46/77] mlx4: Update MSI/MSI-X interrupts enablement
 code

On Wed,  2 Oct 2013 12:49:02 +0200
Alexander Gordeev <agordeev@...hat.com> wrote:

NACK.  This change does not do anything logically as far as I can tell.
pci_enable_msix in the current upstream kernel itself calls
pci_msix_table_size.  The current code yields the same results
as the code suggested below. (i.e., the suggested code has no effect on
optimality).

BTW, pci_msix_table_size never returns a value < 0 (if msix is not
enabled, it returns 0 for the table size), so the (err < 0) check here
is not correct. (I also do not like using "err" here anyway for the
value returned by pci_msix_table_size().  There is no error here, and
it is simply confusing.

-Jack

> As result of recent re-design of the MSI/MSI-X interrupts enabling
> pattern this driver has to be updated to use the new technique to
> obtain a optimal number of MSI/MSI-X interrupts required.
> 
> Signed-off-by: Alexander Gordeev <agordeev@...hat.com>
> ---
>  drivers/net/ethernet/mellanox/mlx4/main.c |   17 ++++++++---------
>  1 files changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx4/main.c
> b/drivers/net/ethernet/mellanox/mlx4/main.c index 60c9f4f..377a5ea
> 100644 --- a/drivers/net/ethernet/mellanox/mlx4/main.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/main.c
> @@ -1852,8 +1852,16 @@ static void mlx4_enable_msi_x(struct mlx4_dev
> *dev) int i;
>  
>  	if (msi_x) {
> +		err = pci_msix_table_size(dev->pdev);
> +		if (err < 0)
> +			goto no_msi;
> +
> +		/* Try if at least 2 vectors are available */
>  		nreq = min_t(int, dev->caps.num_eqs -
> dev->caps.reserved_eqs, nreq);
> +		nreq = min_t(int, nreq, err);
> +		if (nreq < 2)
> +			goto no_msi;
>  
>  		entries = kcalloc(nreq, sizeof *entries, GFP_KERNEL);
>  		if (!entries)
> @@ -1862,17 +1870,8 @@ static void mlx4_enable_msi_x(struct mlx4_dev
> *dev) for (i = 0; i < nreq; ++i)
>  			entries[i].entry = i;
>  
> -	retry:
>  		err = pci_enable_msix(dev->pdev, entries, nreq);
>  		if (err) {
> -			/* Try again if at least 2 vectors are
> available */
> -			if (err > 1) {
> -				mlx4_info(dev, "Requested %d
> vectors, "
> -					  "but only %d MSI-X vectors
> available, "
> -					  "trying again\n", nreq,
> err);
> -				nreq = err;
> -				goto retry;
> -			}
>  			kfree(entries);
>  			goto no_msi;
>  		}

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