lkml.org 
[lkml]   [2019]   [May]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 19/28] locking/lockdep: Optimize irq usage check when marking lock usage bit
On Tue, Apr 30, 2019 at 02:11:48PM +0200, Peter Zijlstra wrote:
> On Fri, Apr 26, 2019 at 02:57:37PM +0800, Yuyang Du wrote:
> > Thanks for review.
> >
> > On Fri, 26 Apr 2019 at 03:32, Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > On Wed, Apr 24, 2019 at 06:19:25PM +0800, Yuyang Du wrote:
> > >
> > > After only a quick read of these next patches; this is the one that
> > > worries me most.
> > >
> > > You did mention Frederic's patches, but I'm not entirely sure you're
> > > aware why he's doing them. He's preparing to split the softirq state
> > > into one state per softirq vector.
> > >
> > > See here:
> > >
> > > https://lkml.kernel.org/r/20190228171242.32144-14-frederic@kernel.org
> > > https://lkml.kernel.org/r/20190228171242.32144-15-frederic@kernel.org
> > >
> > > IOW he's going to massively explode this storage.
> >
> > If I understand correctly, he is not going to.
> >
> > First of all, we can divide the whole usage thing into tracking and checking.
> >
> > Frederic's fine-grained soft vector state is applied to usage
> > tracking, i.e., which specific vectors a lock is used or enabled.
> >
> > But for usage checking, which vectors are does not really matter. So,
> > the current size of the arrays and bitmaps are good enough. Right?
>
> Frederic? My understanding was that he really was going to split the
> whole thing. The moment you allow masking individual soft vectors, you
> get per-vector dependency chains.

Right, so in my patchset there is indeed individual soft vectors masked
so we indeed need per vector checks. For example a lock taken in HRTIMER
softirq shouldn't be a problem if it is concurrently taken while BLOCK softirq
is enabled. And for that we expand the usage_mask so that the 4 bits currently
used for general SOFTIRQ are now multiplied by NR_SOFTIRQ (10) because we need to
track the USED and ENABLED_IN bits for each of them.

The end result is:

4 hard irq bits + 4 * 10 softirq bits + LOCK_USED bit = 45 bits.

Not sure that answers the question as I'm a bit lost in the debate...

\
 
 \ /
  Last update: 2019-05-07 03:48    [W:0.085 / U:0.268 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site