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Re: [RFC PATCH 0/3] xen/spinlock: make recursive spinlocks a dedicated type



On 12/14/22 10:31, Juergen Gross wrote:
On 14.12.22 16:03, Daniel P. Smith wrote:

On 9/10/22 11:49, Juergen Gross wrote:
Instead of being able to use normal spinlocks as recursive ones, too,
make recursive spinlocks a special lock type.

This will make the spinlock structure smaller in production builds and
add type-safety.

Just a little yak shaving, IMHO a spinlock is normally not expected to be recursive. Thus explicitly naming a spinlock as non-recursive I find to be redundant along with being expensive for typing. Whereas a recursive spinlock is the special instance and should have a declarative distinction. Only codifying the recursive type would significantly cut down on the size of the series and still provide equal type and visual clarification.

A "normal" spinlock is non-recursive.

A recursive spinlock in Xen can be either taken recursive, or it can be taken
non-recursive, causing further recursive attempts to spin.

Yes, I understand the current situation.

So the explicit non-recursive locking applies to that special treatment of
recursive spinlocks.

I understand this, but to help clarify what I am saying is that individuals coming from outside Xen would expect is the spinlock family of calls to behave as a non-recursive spinlocks and recursive spinlock family of calls would provide the recursive behavior. Currently Xen's behavior is backwards to this, which this series continues and is a valid approach. Here spinlock and recursive spinlock family of calls are recursive and must use non-recursive spinlock family to have "normal" spinlock behavior. IMHO it would greatly simplify the code and align with the "normal" understanding of spinlocks if instead spin_{lock,locked,unlock} macros were the non-recursive calls and spin_{lock,locked,unlock}_recursive macros were the recursive calls. Then there would only be two suites of calls for spinlocks and a lot less keystrokes for need for most development.

v/r,
dps



 


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