Re: Correct use of ap->lock versus ap->host->lock ?

[Mark Lord <liml@rtr.ca>]

Jeff Garzik wrote:
> Mark Lord wrote:
>> Jeff / Tejun / Alan,
>>
>> I'm trying to sort out the spinlocks in sata_mv.
>>
>> In some places, the existing code uses ap->lock.
>> But in others, notably the interrupt handling, it uses ap->host->lock.
>>
>> This looks buggy to me, and I'm wondering how to make it bulletproof.
> 
> Look closely, there is only one lock.  ata_port does not have a 
> spinlock, just a pointer...
..

Ahh.. in ata_port_alloc().  Thanks.

Mmmm... so this reduces potential parallelism in libata,
meaning we could probably achieve better SMP performance
if the ap->locks were unique for each port.

But at the expense of very tricky and difficult coding
around shared host resources.

Not worth it today for spinning media, but this could be
a big limitation for solid-state media in the near future.

Something to ponder, I guess.

Cheers