On 06/08/2012 02:02 PM, Myron Stowe wrote:
On Fri, Jun 8, 2012 at 11:31 AM, Bjorn Helgaas<bhelgaas@xxxxxxxxxx> wrote:
On Fri, Jun 8, 2012 at 1:01 AM, Xudong Hao<xudong.hao@xxxxxxxxx> wrote:
The series of patches enable LTR and OBFF before device is used by driver, and
introduce a couple of functions to save/restore LTR latency value.
Patch 1/4 introduce new function pci_obff_supported() as pci_ltr_support().
Patch 2/4 enable LTR(Latency tolerance reporting) before device is used by
driver.
Patch 3/4 enable OBFF(optimized buffer flush/fill) before device is used by
driver.
Patch 4/4 introduce a couple of functions pci_save_ltr_value() and
pci_restore_ltr_value() to save and restore LTR latency value, while device is
reset.
We need some justification for these patches. Why do we want them?
Do they improve performance? Reduce power consumption? How have they
been tested? How can we be confident that these features work
correctly on hardware in the field? Should or could the BIOS enable
them itself, based on OEM testing and desire to support these
features?
I too am a little nervous about these changes due to Jesse's earlier response
(see http://marc.info/?l=linux-pci&m=133372610102933&w=2) where he indicated:
"Given how device specific these extensions are, I'd expect you'd need
to know about each specific device anyway, which is why I think the
control belongs in the driver."
Having these features enabled by default may be too aggressive. Not saying it
is not correct - something you may be able to inform us about, especially since
you are with Intel - just make me nervous without further information.
Myron
+1; like AER, I prefer the enablement be in the driver; when/if the
feature has proven itself reliable, then the kernel can enable it by default
In the case of the kernel & driver doing an enable, it won't hurt.
If want hook to disable by boot parameter, the kernel would have to clear
on scan, and put the disable *after* driver probe.
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