Messages in this thread |  | | Date | Sat, 14 Jan 2023 09:42:06 -0800 | From | "Paul E. McKenney" <> | Subject | Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus test) |
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On Fri, Jan 13, 2023 at 05:05:11PM +0000, Jonas Oberhauser wrote: > -----Original Message----- > From: Alan Stern [mailto:stern@rowland.harvard.edu] > Sent: Friday, January 13, 2023 5:38 PM > > > Strictly speaking, this is not right. It should say: For each process/CPU/task/whatever, an RCU grace period includes at least one moment in time during which that process is not within an RCU read-side critical section. There does not have to be any single moment during which no processes are executing a critical section. > > I see. I guess the other thing is more like a quiescent period.
"Quiescent period" was in fact my original name for "grace period" back in the day, but a chorus of objections eventually prompted me to instead label it a "grace period".
Perhaps you have given an improved rationale for their objections. ;-)
> I > think the fact that RCU/safe memory reclamation(SMR) don't require a > quiescent period is an important distinction, and even though we have > our own SMR I never thought too deeply about this distinction.
If you want non-abysmal performance and scalability on modern hardware, the distinction is critically important. After all, the speed of light really is finite, and atoms are of non-zero size. And to the complete surprise of my forty-years-ago self, these laws of physics seriously constrain modern computing devices.
Thanx, Paul
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