Hi Ben, Steph,
On Wed, Jul 16, 2014 at 4:31 AM, Ben Coman <b...@openinworld.com> wrote: > stepharo wrote: > >> Hi eliot >> >> Thanks! >> I'm really eager to read about the new become implementation. >> > > There is this... > http://www.mirandabanda.org/cogblog/2013/09/13/lazy- > become-and-a-partial-read-barrier/ yes, but I've removed all the scanning of the class table post become. So that post is inaccurate now. Steph, I plan to update the SpurMemoryManager class comment and that post soon to reflect the current design. > cheers -ben > > > I could not fully understand the following but this is exciting to know >> that you removed complexity. >> >> Stef >> >> "The read barriers on method lookup (of the methodClass association in >> super >> sends, of the superclass link, of method dictionaries, method dictionary >> arrays, >> selectors and methods is cheap. So replace scanning classes and method >> dictionaries in the class table post become with read marriewrs on >> methodClass, >> superclass and method dictionary etc on lookup. >> >> The read barrier on an object from which we are going to fetch state >> (such as a >> class or method dictionary) is essentially free on modern machines >> because the >> class index and the state very likely share a cache line, and the >> register code >> for testing is so cheap compared to memory access. Further the read >> barrier on >> selectors is cheap because the method lookup cache is effective in >> reducing the >> number of message lookups and because nil entries need no check. >> >> So nuke all the followNecessaryForwardingInMethod: machinery including >> the >> cmUsesMethodClass hack. Nuke scanClassPostBecome:effects:." >> >> >> >> >> On 15/7/14 21:58, Eliot Miranda wrote: >> >>> ...at http://www.mirandabanda.org/files/Cog/VM/VM.r3041/. >>> >>> >>> The principal changes are fixing a performance regression in the 3040 >>> VMs, fixing some Spur bugs in primitiveClone/shallowCopy, and radically >>> simplifying the Spur become implementation, >>> trading the elimination of lots of post-become class table scanning for >>> adding read barriers to class hierarchy method lookup. >>> >>> >>> CogVM source as per VMMaker.oscog-eem.820/r3041 >>> >>> Put the handling of the cloning of cogged methods in the clone: >>> implementations, >>> removing it from the primitive. Add it to the pinning clone too. >>> >>> Specialize the store check trampoline generation. >>> Move it down to the relevant object representations. >>> >>> Move setting of isRemembered flag to true into SpurGenerationScavenger>> >>> remember:. Inline possibleRootStoreInto: (given that remember: is /not/ >>> inlined. Call remember directly from the ceStoreCheckTrampoline, and >>> hence have remember: answer its argument. >>> >>> Fix localization bug. Variables in initialize methods were not >>> considered >>> references (cuz there are excluded). This caused VMMaker.oscog-eem.816's >>> extraction of zero/false vars to StackInterpreter>>#initialize to cause >>> nextPollUsecs to be localized to checkForEventsMayContextSwitch:. >>> >>> Spur: >>> Fix bug in scanClassPostBecome:effects: with new lazy >>> selector following policy by... throwing it all away. >>> >>> The read barriers on method lookup (of the methodClass association in >>> super >>> sends, of the superclass link, of method dictionaries, method dictionary >>> arrays, >>> selectors and methods is cheap. So replace scanning classes and method >>> dictionaries in the class table post become with read marriewrs on >>> methodClass, >>> superclass and method dictionary etc on lookup. >>> >>> The read barrier on an object from which we are going to fetch state >>> (such as a >>> class or method dictionary) is essentially free on modern machines >>> because the >>> class index and the state very likely share a cache line, and the >>> register code >>> for testing is so cheap compared to memory access. Further the read >>> barrier on >>> selectors is cheap because the method lookup cache is effective in >>> reducing the >>> number of message lookups and because nil entries need no check. >>> >>> So nuke all the followNecessaryForwardingInMethod: machinery including >>> the >>> cmUsesMethodClass hack. Nuke scanClassPostBecome:effects:. >>> >>> Rip out the forwardingCount: measurement code. It causes >>> bad performance regressions (due to failing inlines?) >>> >>> Clean up, e.g. replace followNonImmediateField:ofObject: >>> uses with followObjField:ofObject:. >>> >>> canPinObjects can be inlined. >>> >>> >>> -- >>> best, >>> Eliot >>> >> >> >> >> > > -- best, Eliot
