New Cog VMs available

> ...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

> 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
>
>
>