Messages in this thread | | | Date | Tue, 7 May 2019 03:47:14 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 19/28] locking/lockdep: Optimize irq usage check when marking lock usage bit |
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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...
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