Re: [PATCH 11/12] libata: use IRQ expecting
From: Jeff Garzik
Date: Fri Jun 25 2010 - 23:52:38 EST
On 06/25/2010 03:44 AM, Tejun Heo wrote:
I still think calling unexpect_irq() from ata_qc_complete() is correct
as ata_qc_complete() is always a good indicator of completion events.
No, it's not. ata_qc_complete() is an indicator that _one_ completion
event occurred, not _all_ completion events for that port.
Converting drivers to use ata_qc_complete_multiple() completely misses
the point: ata_qc_complete_multiple() is doing exactly the same thing
as those drivers: calling ata_qc_complete() in a loop.
ata_qc_complete() is -- as its name implies -- completing a single qc.
Your patch introduces an unconditional controller-wide unexpect_irq()
call. It's a layering violation.
You can trivially trace through ata_qc_complete_multiple() after patch
#11 is applied, and see the result... for $N completion bits passed to
ata_qc_complete_multiple(), you call
in rapid succession $N times, once for each ata_qc_complete() call in
the loop of ata_qc_complete_multiple(). For something that is not
needed for modern SATA controllers.
The preferred solution would be something that only touches legacy
*) create ata_port_complete(), with the implementation
*) then call ata_port_complete() in the legacy code that needs
We don't want to burden modern SATA drivers with the overhead of
dealing with silly PATA/SATA1 legacy irq nastiness, particularly the
ugliness of calling
unexpect_irq() + expect_irq()
for a number of NCQ commands, in a tight loop!
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