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

[Vladimir Kondratyev]

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