On 1/17/24 02:43, Jakub Kicinski wrote:
On Tue, 16 Jan 2024 14:38:47 -0500 Sasha Levin wrote:
Mirsad proposed a patch to reduce the number of spinlock lock/unlock
operations and the function code size. This can be further improved
because the function sets a consecutive register block.
Clearly a noop and a lot of LoC changed. I vote to drop this from
the backport.
Dear Jakub,
I will not argue with a senior developer, but please let me plead for the
cause.
There are a couple of issues here:
1. Heiner's patch generates smaller and faster code, with 100+
spin_lock_irqsave()/spin_unlock_restore() pairs less.
According to this table:
[1] https://mirrors.edge.kernel.org/pub/linux/kernel/people/paulmck/perfbook/perfbook-1c.2023.06.11a.pdf#table.3.1
The cost of single lock can be 15.4 - 101.9 ns (for the example CPU),
so total savings would be 1709 - 11310 ns. But as the event of PHY power
down is not frequent, this might be a insignificant saving indeed.
2. Why I had advertised atomic programming of RTL registers in the first
place?
The mac_ocp_lock was introduced recently:
commit 91c8643578a21e435c412ffbe902bb4b4773e262
Author: Heiner Kallweit <hkallweit1@xxxxxxxxx>
Date: Mon Mar 6 22:23:15 2023 +0100
r8169: use spinlock to protect mac ocp register access
For disabling ASPM during NAPI poll we'll have to access mac ocp
registers in atomic context. This could result in races because
a mac ocp read consists of a write to register OCPDR, followed
by a read from the same register. Therefore add a spinlock to
protect access to mac ocp registers.
Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
Tested-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
Tested-by: Holger Hoffstätte <holger@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Heiner Kallweit <hkallweit1@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Well, the answer is in the question - the very need for protecting the access
to RTL_W(8|16|32) with locks comes from the fact that something was accessing
the RTL card asynchronously.
Forgive me if this is a stupid question ...
Now - do we have a guarantee that the card will not be used asynchronously
half-programmed from something else in that case, leading to another spurious
lockup?
IMHO, shouldn't the entire reprogramming of PHY down recovery of the RTL 8411b
be done atomically, under a single spin_lock_irqsave()/spin_unlock_irqrestore()
pair?
Best regards,
Mirsad Todorovac
--
CARNet system engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb
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