lkml.org 
[lkml]   [2022]   [May]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/2] locking/qrwlock: Reduce cacheline contention for rwlocks used in interrupt context
On Wed, May 11, 2022 at 08:44:55AM -0400, Waiman Long wrote:

> > I'm confused; prior to this change:
> >
> > CPU0 CPU1
> >
> > write_lock_irq(&l)
> > read_lock(&l)
> > <INRQ>
> > read_lock(&l)
> > ...
> >
> > was not deadlock, but now it would AFAICT.
>
> Oh you are right. I missed that scenario in my analysis. My bad.

No worries; I suppose we can also still do something like:

void queued_read_lock_slowpath(struct qrwlock *lock, int cnts)
{
/*
* the big comment
*/
if (unlikely(in_interrupt())) {
/*
* If not write-locked, insta-grant the reader
*/
if (!(cnts & _QW_LOCKED))
return;

/*
* otherwise, wait for the writer to go away.
*/
atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
return;
}

...
}

Which saves one load in some cases... not sure it's worth it though.

\
 
 \ /
  Last update: 2022-05-11 15:36    [W:0.072 / U:0.472 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site