Re: [RFC] time: xtime_lock is held too long

[Henrik Rydberg]

Hi Eric,

> > Defeating seqlock power? My thoughts are that seqlocks are nice
> > lightweight reader/writer locks that avoid writer starvation. You seem
> > to be trying to redefine or extend them to be something else which is
> > more subtle. 
> > 
> 
> All I am trying to explain is that a seqlock is a compound of two
> things : One spinlock to synchronize writers among themselves, one
> seqcount to synchronize readers with a writer.
> 
> But the API provides only a compound one. Writer uses the whole locking,
> while it would be nice to be able to separate the two steps. Note that
> because write_seqlock() and write_sequnlock() are inlined, this would
> not increase text size.

The separate writer and reader idea also came up in the input
subsystem about a year ago, to adress the one-writer-many-readers
situation. The patch went a few rounds on lkml
(https://lkml.org/lkml/2010/6/20/87), but the final version included
below got dropped because of an unrelated problem with the (evdev)
usecase. Perhaps it is useful in this setting?

Cheers,
Henrik