On Wed, Sep 29, 2021 at 11:37:01AM -0700, Paul E. McKenney wrote: > On Wed, Sep 29, 2021 at 05:17:31PM +0200, Peter Zijlstra wrote: > The CT_SEQ_WORK bit means neither idle nor nohz_full user, correct? That bit is indeed independent, it can get set remotely by cmpxchg when in user/eqs state and will be tested and (eventually) cleared when leaving user/eqs state. > So let's see if I intuited the decoder ring, where "kernel" means that > portion of the kernel that is non-noinstr... > > CT_SEQ_WORK CT_SEQ_NMI CT_SEQ_USER Description? > 0 0 0 Idle or non-nohz_full user > 0 0 1 nohz_full user > 0 1 0 NMI from 0,0,0 > 0 1 1 NMI from 0,0,1 > 1 0 0 Non-idle kernel > 1 0 1 Cannot happen? > 1 1 0 NMI from 1,0,1 > 1 1 1 NMI from cannot happen > > And of course if a state cannot happen, Murphy says that you will take > an NMI in that state. Urgh, you have the bits the 'wrong' way around :-) MSB 3210 |-------|||| Where [MSB-3] is the actual sequence number, [21] is the state and [0] is the work-pending bit. The table for [21] is like: USER NMI 0 0 kernel 0 1 kernel took nmi 1 0 user 1 1 user took nmi So effectively EQS is 10 only, the other 3 states are kernel.
