From: Hannes Reinecke <hare@suse.de>
To: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-pci@vger.kernel.org,
Jordan Hargrave <Jordan_Hargrave@dell.com>,
Babu Moger <babu.moger@oracle.com>,
Alexander Duyck <alexander.duyck@gmail.com>
Subject: Re: [PATCH v4 11/11] PCI: Sleep rather than busy-wait for VPD access completion
Date: Tue, 23 Feb 2016 20:25:26 +0800 [thread overview]
Message-ID: <56CC4FB6.5020709@suse.de> (raw)
In-Reply-To: <20160223004742.10635.55287.stgit@bhelgaas-glaptop2.roam.corp.google.com>
On 02/23/2016 08:47 AM, Bjorn Helgaas wrote:
> Use usleep_range() instead of udelay() while waiting for a VPD access to
> complete. This is not a performance path, so no need to hog the CPU.
>
> Rationale for usleep_range() parameters:
>
> We clear PCI_VPD_ADDR_F for a read (or set it for a write), then wait for
> the device to change it. For a device that updates PCI_VPD_ADDR between
> our config write and subsequent config read, we won't sleep at all and
> can get the device's maximum rate.
>
> Sleeping a minimum of 10 usec per 4-byte access limits throughput to
> about 400Kbytes/second. VPD is small (32K bytes at most), and most
> devices use only a fraction of that.
>
> We back off exponentially up to 1024 usec per iteration. If we reach
> 1024, we've already waited up to 1008 usec (16 + 32 + ... + 512), so if
> we miss an update and wait an extra 1024 usec, we can still get about 1/2
> of the device's maximum rate.
>
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> ---
Reviewed-by: Hannes Reinecke <hare@suse.com>
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
next prev parent reply other threads:[~2016-02-23 12:25 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-23 0:46 [PATCH v4 00/11] PCI VPD access fixes Bjorn Helgaas
2016-02-23 0:46 ` [PATCH v4 01/11] PCI: Update VPD definitions Bjorn Helgaas
2016-02-23 0:46 ` [PATCH v4 02/11] PCI: Allow access to VPD attributes with size 0 Bjorn Helgaas
2016-02-23 0:46 ` [PATCH v4 03/11] PCI: Use bitfield instead of bool for struct pci_vpd_pci22.busy Bjorn Helgaas
2016-02-23 12:19 ` Hannes Reinecke
2016-02-23 0:46 ` [PATCH v4 04/11] PCI: Determine actual VPD size on first access Bjorn Helgaas
2016-02-23 0:47 ` [PATCH v4 05/11] FIXME need bugzilla link Bjorn Helgaas
2016-02-23 0:47 ` [PATCH v4 06/11] PCI: Move pci_read_vpd() and pci_write_vpd() close to other VPD code Bjorn Helgaas
2016-02-23 12:20 ` Hannes Reinecke
2016-02-23 0:47 ` [PATCH v4 07/11] PCI: Move pci_vpd_release() from header file to pci/access.c Bjorn Helgaas
2016-02-23 12:21 ` Hannes Reinecke
2016-02-23 0:47 ` [PATCH v4 08/11] PCI: Remove struct pci_vpd_ops.release function pointer Bjorn Helgaas
2016-02-23 12:22 ` Hannes Reinecke
2016-02-23 0:47 ` [PATCH v4 09/11] PCI: Rename VPD symbols to remove unnecessary "pci22" Bjorn Helgaas
2016-02-23 12:23 ` Hannes Reinecke
2016-02-23 0:47 ` [PATCH v4 10/11] PCI: Fold struct pci_vpd_pci22 into struct pci_vpd Bjorn Helgaas
2016-02-23 12:24 ` Hannes Reinecke
2016-02-23 0:47 ` [PATCH v4 11/11] PCI: Sleep rather than busy-wait for VPD access completion Bjorn Helgaas
2016-02-23 12:25 ` Hannes Reinecke [this message]
2016-02-23 14:07 ` [PATCH v4 00/11] PCI VPD access fixes Bjorn Helgaas
2016-02-23 21:48 ` Hannes Reinecke
2016-02-23 22:36 ` Bjorn Helgaas
2016-02-24 0:30 ` Hannes Reinecke
2016-02-24 0:45 ` Bjorn Helgaas
2016-02-23 17:11 ` Bjorn Helgaas
2016-02-24 4:52 ` Seymour, Shane M
2016-02-29 22:36 ` Babu Moger
2016-02-29 17:27 ` Babu Moger
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