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Date: Fri, 11 Oct 2013 16:29:39 -0400 From: Mark Lord <kernel@...rt.ca> To: Alexander Gordeev <agordeev@...hat.com> CC: "H. Peter Anvin" <hpa@...or.com>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>, Ralf Baechle <ralf@...ux-mips.org>, Michael Ellerman <michael@...erman.id.au>, 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 00/77] Re-design MSI/MSI-X interrupts enablement pattern On 13-10-11 04:41 AM, Alexander Gordeev wrote: > On Thu, Oct 10, 2013 at 07:17:18PM -0400, Mark Lord wrote: >> Just to help us all understand "the loop" issue.. >> >> Here's an example of driver code which uses the existing MSI-X interfaces, >> for a device which can work with either 16, 8, 4, 2, or 1 MSI-X interrupt. >> This is from a new driver I'm working on right now: .. > Now, this is a loop-free alternative: > > static int xx_alloc_msix_irqs(struct xx_dev *dev, int nvec) > { > nvec = roundup_pow_of_two(nvec); /* assume 0 > nvec <= 16 */ > > xx_disable_all_irqs(dev); > > pci_lock_msi(dev->pdev); > > rc = pci_get_msix_limit(dev->pdev, nvec); > if (rc < 0) > goto err; > > nvec = min(nvec, rc); /* if limit is more than requested */ > nvec = rounddown_pow_of_two(nvec); /* (a) */ > > xx_prep_for_msix_vectors(dev, nvec); > > rc = pci_enable_msix(dev->pdev, dev->irqs, nvec); /* (b) */ > if (rc < 0) > goto err; > > pci_unlock_msi(dev->pdev); > > dev->num_vectors = nvec; /* (b) */ > return 0; > > err: > pci_unlock_msi(dev->pdev); > > kerr(dev->name, "pci_enable_msix() failed, err=%d", rc); > dev->num_vectors = 0; > return rc; > } That would still need a loop, to handle the natural race between the calls to pci_get_msix_limit() and pci_enable_msix() -- the driver and device can and should fall back to a smaller number of vectors when pci_enable_msix() fails. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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