svn commit: r354322 - head/sys/dev/ichiic

[Konstantin Belousov]

On Mon, Nov 04, 2019 at 01:46:14AM +0300, Vladimir Kondratyev wrote:
> On 04.11.2019 01:02, Konstantin Belousov wrote:
> > On Sun, Nov 03, 2019 at 09:17:51PM +0000, Vladimir Kondratyev wrote:
> >> Author: wulf
> >> Date: Sun Nov  3 21:17:50 2019
> >> New Revision: 354322
> >> URL: https://svnweb.freebsd.org/changeset/base/354322
> >>
> >> Log:
> >>   [ig4] Convert ithread interrupt handler to filter based one.
> > And why ?
> >
> > You need some reason to use filters/spinlocks, otherwise it only
> > taxes system latency.
> 
> 
> The only thing ig4 interrupt handler does is a waking up the user
> thread, so postponing it to ithread looks like a wasting of CPU cycles.
> 
> Spinlock here is acting as condition variable not as a data protection
> lock. It is taken around msleep(). I can replace it with cv_* calls if
> current usage confuses someone
> 
> Ig4 access is serialized with sx lock so it is impossible to get any
> congestion on spinlock
> 
You need to lock the same spinlock in the sleeping thread and in the
interrupt context.

I do not remember why these drivers ended up using sx for their main data
synchronization, I suspect it was due to copyouts.