On Mon, May 16, 2016 at 10:46:38AM +0100, Matt Fleming wrote: > > > > > > - rq->clock_skip_update = 0; > > > + /* Clear ACT, preserve everything else */ > > > + rq->clock_update_flags ^= RQCF_ACT_SKIP; > > > > The comment says "Clear ACT", but this is really xor, and I am not sure > > this is even what you want. > > Urgh, you're right. I'm not sure what I was thinking when I wrote > that.
It happens, ;) > > In addition, would it be simpler to do this? > > > > update_rq_clock() > > if (flags & RQCF_ACT_SKIP) > > flags <<= 1; /* effective skip is an update */ > > return; > > > > flags = RQCF_UPDATED; > > No because if someone calls rq_clock() immediately after __schedule(), > or even immediately after we clear RQCF_ACT_SKIP in __schedule(), we > should trigger a warning since the clock has not actually been > updated. Well, I don't know how concurrent it can be, but aren't both update and read synchronized by rq->lock? So I don't understand the latter case, and the former should be addressed (missing its own update?).
