[PATCH] usb: ehci: make HC see up-to-date qh/qtd descriptor ASAP

[Pandita, Vikram]

On Thu, Sep 8, 2011 at 3:41 PM, Mark Salter <msalter at redhat.com> wrote:
> On Wed, 2011-08-31 at 20:35 +0100, Will Deacon wrote:
>> On Wed, Aug 31, 2011 at 07:19:33PM +0100, Rob Herring wrote:
>> > On 08/31/2011 12:51 PM, Will Deacon wrote:
>> > > Another thing that Marc and I tried on OMAP4 was not bringing up the secondary
>> > > CPU during boot (by commenting out most of smp_init). In this case, I/O
>> > > performance was good until we tried to online the secondary CPU. The online
>> > > failed but after that the I/O performance was certainly degraded.
>> > >
>> >
>> > Was the SCU enabled at that point? One diff between nosmp boot and
>> > offlining the 2nd core would be that the SCU remains enabled in the
>> > latter case. I think the SCU does not get enabled for nosmp.
>>
>> Our rudimentary test (printing out the SCU control register during boot)
>> showed that it *was* enabled for nosmp. I think this is due to the secure
>> world having to do that on OMAP so it's probably not true for other
>> platforms.
>
> I've done a little test and found that turning on the MMU of the second
> core causes the problem to show up. I patched head.S so I stopped the
> second core in an infinite loop just before turning on the MMU. The
> system continues booting on core#0 and I see ~20MB/s with hdparm -t to
> an attached usb disk. Same setup but with second core being stopped with
> infinite loop just after MMU is enabled shows ~5MB/s. So whatever is
> going wrong, its not because of anything the second core is doing beyond
> turning on its MMU and doing an empty loop.

what was the final take on the optimization?
Excuse if i could not follow the whole thread - could someone
summarize for the benefit of many.

Thanks

>
> --Mark
>
>
>
>
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