Re: RFR: 8276096: Simplify Unsafe.{load|store}Fence fallbacks by delegating to fullFence [v2]
On Mon, 1 Nov 2021 07:36:53 GMT, Aleksey Shipilev wrote:
>> `Unsafe.{load|store}Fence` falls back to `unsafe.cpp` for
>> `OrderAccess::{acquire|release}Fence()`. It seems too heavy-handed
>> (useless?) to call to runtime for a single memory barrier. We can simplify
>> the native `Unsafe` interface by falling back to `fullFence` when
>> `{load|store}Fence` intrinsics are not available. This would be similar to
>> what `Unsafe.{loadLoad|storeStore}Fences` do.
>>
>> This is the behavior of these intrinsics now, on x86_64, using benchmarks
>> from JDK-8276054:
>>
>>
>> Benchmark Mode Cnt Score Error Units
>>
>> # Default
>> Single.acquire avgt3 0.407 ± 0.060 ns/op
>> Single.fullavgt3 4.693 ± 0.005 ns/op
>> Single.loadLoadavgt3 0.415 ± 0.095 ns/op
>> Single.plain avgt3 0.406 ± 0.002 ns/op
>> Single.release avgt3 0.408 ± 0.047 ns/op
>> Single.storeStore avgt3 0.408 ± 0.043 ns/op
>>
>> # -XX:DisableIntrinsic=_storeFence
>> Single.acquire avgt3 0.408 ± 0.016 ns/op
>> Single.fullavgt3 4.694 ± 0.002 ns/op
>> Single.loadLoadavgt3 0.406 ± 0.002 ns/op
>> Single.plain avgt3 0.406 ± 0.001 ns/op
>> Single.release avgt3 4.694 ± 0.003 ns/op <--- upgraded to full
>> Single.storeStore avgt3 4.690 ± 0.005 ns/op <--- upgraded to full
>>
>> # -XX:DisableIntrinsic=_loadFence
>> Single.acquire avgt3 4.691 ± 0.001 ns/op <--- upgraded to full
>> Single.fullavgt3 4.693 ± 0.009 ns/op
>> Single.loadLoadavgt3 4.693 ± 0.013 ns/op <--- upgraded to full
>> Single.plain avgt3 0.408 ± 0.072 ns/op
>> Single.release avgt3 0.415 ± 0.016 ns/op
>> Single.storeStore avgt3 0.416 ± 0.041 ns/op
>>
>> # -XX:DisableIntrinsic=_fullFence
>> Single.acquire avgt3 0.406 ± 0.014 ns/op
>> Single.fullavgt3 15.836 ± 0.151 ns/op <--- calls runtime
>> Single.loadLoadavgt3 0.406 ± 0.001 ns/op
>> Single.plain avgt3 0.426 ± 0.361 ns/op
>> Single.release avgt3 0.407 ± 0.021 ns/op
>> Single.storeStore avgt3 0.410 ± 0.061 ns/op
>>
>> # -XX:DisableIntrinsic=_fullFence,_loadFence
>> Single.acquire avgt3 15.822 ± 0.282 ns/op <--- upgraded, calls
>> runtime
>> Single.fullavgt3 15.851 ± 0.127 ns/op <--- calls runtime
>> Single.loadLoadavgt3 15.829 ± 0.045 ns/op <--- upgraded, calls
>> runtime
>> Single.plain avgt3 0.406 ± 0.001 ns/op
>> Single.release avgt3 0.414 ± 0.156 ns/op
>> Single.storeStore avgt3 0.422 ± 0.452 ns/op
>>
>> # -XX:DisableIntrinsic=_fullFence,_storeFence
>> Single.acquire avgt3 0.407 ± 0.016 ns/op
>> Single.fullavgt3 15.347 ± 6.783 ns/op <--- calls runtime
>> Single.loadLoadavgt3 0.406 ± 0.001 ns/op
>> Single.plain avgt3 0.406 ± 0.002 ns/op
>> Single.release avgt3 15.828 ± 0.019 ns/op <--- upgraded, calls
>> runtime
>> Single.storeStore avgt3 15.834 ± 0.045 ns/op <--- upgraded, calls
>> runtime
>>
>> # -XX:DisableIntrinsic=_fullFence,_loadFence,_storeFence
>> Single.acquire avgt3 15.838 ± 0.030 ns/op <--- upgraded, calls
>> runtime
>> Single.fullavgt3 15.854 ± 0.277 ns/op <--- calls runtime
>> Single.loadLoadavgt3 15.826 ± 0.160 ns/op <--- upgraded, calls
>> runtime
>> Single.plain avgt3 0.406 ± 0.003 ns/op
>> Single.release avgt3 15.838 ± 0.019 ns/op <--- upgraded, calls
>> runtime
>> Single.storeStore avgt3 15.844 ± 0.104 ns/op <--- upgraded, calls
>> runtime
>>
>>
>> Additional testing:
>> - [x] Linux x86_64 fastdebug `tier1`
>
> Aleksey Shipilev has updated the pull request incrementally with one
> additional commit since the last revision:
>
> Restore RN for fullFence
Thanks!
-
PR: https://git.openjdk.java.net/jdk/pull/6149
Re: RFR: 8276096: Simplify Unsafe.{load|store}Fence fallbacks by delegating to fullFence [v2]
On Mon, 1 Nov 2021 07:36:53 GMT, Aleksey Shipilev wrote:
>> `Unsafe.{load|store}Fence` falls back to `unsafe.cpp` for
>> `OrderAccess::{acquire|release}Fence()`. It seems too heavy-handed
>> (useless?) to call to runtime for a single memory barrier. We can simplify
>> the native `Unsafe` interface by falling back to `fullFence` when
>> `{load|store}Fence` intrinsics are not available. This would be similar to
>> what `Unsafe.{loadLoad|storeStore}Fences` do.
>>
>> This is the behavior of these intrinsics now, on x86_64, using benchmarks
>> from JDK-8276054:
>>
>>
>> Benchmark Mode Cnt Score Error Units
>>
>> # Default
>> Single.acquire avgt3 0.407 ± 0.060 ns/op
>> Single.fullavgt3 4.693 ± 0.005 ns/op
>> Single.loadLoadavgt3 0.415 ± 0.095 ns/op
>> Single.plain avgt3 0.406 ± 0.002 ns/op
>> Single.release avgt3 0.408 ± 0.047 ns/op
>> Single.storeStore avgt3 0.408 ± 0.043 ns/op
>>
>> # -XX:DisableIntrinsic=_storeFence
>> Single.acquire avgt3 0.408 ± 0.016 ns/op
>> Single.fullavgt3 4.694 ± 0.002 ns/op
>> Single.loadLoadavgt3 0.406 ± 0.002 ns/op
>> Single.plain avgt3 0.406 ± 0.001 ns/op
>> Single.release avgt3 4.694 ± 0.003 ns/op <--- upgraded to full
>> Single.storeStore avgt3 4.690 ± 0.005 ns/op <--- upgraded to full
>>
>> # -XX:DisableIntrinsic=_loadFence
>> Single.acquire avgt3 4.691 ± 0.001 ns/op <--- upgraded to full
>> Single.fullavgt3 4.693 ± 0.009 ns/op
>> Single.loadLoadavgt3 4.693 ± 0.013 ns/op <--- upgraded to full
>> Single.plain avgt3 0.408 ± 0.072 ns/op
>> Single.release avgt3 0.415 ± 0.016 ns/op
>> Single.storeStore avgt3 0.416 ± 0.041 ns/op
>>
>> # -XX:DisableIntrinsic=_fullFence
>> Single.acquire avgt3 0.406 ± 0.014 ns/op
>> Single.fullavgt3 15.836 ± 0.151 ns/op <--- calls runtime
>> Single.loadLoadavgt3 0.406 ± 0.001 ns/op
>> Single.plain avgt3 0.426 ± 0.361 ns/op
>> Single.release avgt3 0.407 ± 0.021 ns/op
>> Single.storeStore avgt3 0.410 ± 0.061 ns/op
>>
>> # -XX:DisableIntrinsic=_fullFence,_loadFence
>> Single.acquire avgt3 15.822 ± 0.282 ns/op <--- upgraded, calls
>> runtime
>> Single.fullavgt3 15.851 ± 0.127 ns/op <--- calls runtime
>> Single.loadLoadavgt3 15.829 ± 0.045 ns/op <--- upgraded, calls
>> runtime
>> Single.plain avgt3 0.406 ± 0.001 ns/op
>> Single.release avgt3 0.414 ± 0.156 ns/op
>> Single.storeStore avgt3 0.422 ± 0.452 ns/op
>>
>> # -XX:DisableIntrinsic=_fullFence,_storeFence
>> Single.acquire avgt3 0.407 ± 0.016 ns/op
>> Single.fullavgt3 15.347 ± 6.783 ns/op <--- calls runtime
>> Single.loadLoadavgt3 0.406 ± 0.001 ns/op
>> Single.plain avgt3 0.406 ± 0.002 ns/op
>> Single.release avgt3 15.828 ± 0.019 ns/op <--- upgraded, calls
>> runtime
>> Single.storeStore avgt3 15.834 ± 0.045 ns/op <--- upgraded, calls
>> runtime
>>
>> # -XX:DisableIntrinsic=_fullFence,_loadFence,_storeFence
>> Single.acquire avgt3 15.838 ± 0.030 ns/op <--- upgraded, calls
>> runtime
>> Single.fullavgt3 15.854 ± 0.277 ns/op <--- calls runtime
>> Single.loadLoadavgt3 15.826 ± 0.160 ns/op <--- upgraded, calls
>> runtime
>> Single.plain avgt3 0.406 ± 0.003 ns/op
>> Single.release avgt3 15.838 ± 0.019 ns/op <--- upgraded, calls
>> runtime
>> Single.storeStore avgt3 15.844 ± 0.104 ns/op <--- upgraded, calls
>> runtime
>>
>>
>> Additional testing:
>> - [x] Linux x86_64 fastdebug `tier1`
>
> Aleksey Shipilev has updated the pull request incrementally with one
> additional commit since the last revision:
>
> Restore RN for fullFence
Marked as reviewed by dholmes (Reviewer).
-
PR: https://git.openjdk.java.net/jdk/pull/6149
Re: RFR: 8276096: Simplify Unsafe.{load|store}Fence fallbacks by delegating to fullFence [v2]
On Mon, 1 Nov 2021 07:32:18 GMT, Aleksey Shipilev wrote: >> src/hotspot/share/classfile/vmIntrinsics.hpp line 526: >> >>> 524:do_name( storeFence_name, >>> "storeFence")\ >>> 525:do_alias(storeFence_signature, >>> void_method_signature) \ >>> 526: do_intrinsic(_fullFence,jdk_internal_misc_Unsafe, >>> fullFence_name, fullFence_signature, F_R) \ >> >> Why did you drop the N from F_RN? AFAICS the fullFence method is still >> native. > > Good spot! That's indeed incorrect, fixed in new commit. I am surprised > `CheckIntrinsics` did not found this discrepancy. I believe "native" flags > are not checked at all? For example, existing `_hashCode` intrinsic is also > `F_R`, while it covers the native `java.lang.Object::hashCode`. I try to beef > up those checks separately. This `CheckIntrinsics` oddity is handled by #6187. - PR: https://git.openjdk.java.net/jdk/pull/6149
Re: RFR: 8276096: Simplify Unsafe.{load|store}Fence fallbacks by delegating to fullFence [v2]
On Mon, 1 Nov 2021 02:09:19 GMT, David Holmes wrote: >> Aleksey Shipilev has updated the pull request incrementally with one >> additional commit since the last revision: >> >> Restore RN for fullFence > > src/hotspot/share/classfile/vmIntrinsics.hpp line 526: > >> 524:do_name( storeFence_name, >> "storeFence")\ >> 525:do_alias(storeFence_signature, >> void_method_signature) \ >> 526: do_intrinsic(_fullFence,jdk_internal_misc_Unsafe, >> fullFence_name, fullFence_signature, F_R) \ > > Why did you drop the N from F_RN? AFAICS the fullFence method is still native. Good spot! That's indeed incorrect, fixed in new commit. I am surprised `CheckIntrinsics` did not found this discrepancy. I believe "native" flags are not checked at all? For example, existing `_hashCode` intrinsic is also `F_R`, while it covers the native `java.lang.Object::hashCode`. I try to beef up those checks separately. - PR: https://git.openjdk.java.net/jdk/pull/6149
Re: RFR: 8276096: Simplify Unsafe.{load|store}Fence fallbacks by delegating to fullFence [v2]
> `Unsafe.{load|store}Fence` falls back to `unsafe.cpp` for
> `OrderAccess::{acquire|release}Fence()`. It seems too heavy-handed (useless?)
> to call to runtime for a single memory barrier. We can simplify the native
> `Unsafe` interface by falling back to `fullFence` when `{load|store}Fence`
> intrinsics are not available. This would be similar to what
> `Unsafe.{loadLoad|storeStore}Fences` do.
>
> This is the behavior of these intrinsics now, on x86_64, using benchmarks
> from JDK-8276054:
>
>
> Benchmark Mode Cnt Score Error Units
>
> # Default
> Single.acquire avgt3 0.407 ± 0.060 ns/op
> Single.fullavgt3 4.693 ± 0.005 ns/op
> Single.loadLoadavgt3 0.415 ± 0.095 ns/op
> Single.plain avgt3 0.406 ± 0.002 ns/op
> Single.release avgt3 0.408 ± 0.047 ns/op
> Single.storeStore avgt3 0.408 ± 0.043 ns/op
>
> # -XX:DisableIntrinsic=_storeFence
> Single.acquire avgt3 0.408 ± 0.016 ns/op
> Single.fullavgt3 4.694 ± 0.002 ns/op
> Single.loadLoadavgt3 0.406 ± 0.002 ns/op
> Single.plain avgt3 0.406 ± 0.001 ns/op
> Single.release avgt3 4.694 ± 0.003 ns/op <--- upgraded to full
> Single.storeStore avgt3 4.690 ± 0.005 ns/op <--- upgraded to full
>
> # -XX:DisableIntrinsic=_loadFence
> Single.acquire avgt3 4.691 ± 0.001 ns/op <--- upgraded to full
> Single.fullavgt3 4.693 ± 0.009 ns/op
> Single.loadLoadavgt3 4.693 ± 0.013 ns/op <--- upgraded to full
> Single.plain avgt3 0.408 ± 0.072 ns/op
> Single.release avgt3 0.415 ± 0.016 ns/op
> Single.storeStore avgt3 0.416 ± 0.041 ns/op
>
> # -XX:DisableIntrinsic=_fullFence
> Single.acquire avgt3 0.406 ± 0.014 ns/op
> Single.fullavgt3 15.836 ± 0.151 ns/op <--- calls runtime
> Single.loadLoadavgt3 0.406 ± 0.001 ns/op
> Single.plain avgt3 0.426 ± 0.361 ns/op
> Single.release avgt3 0.407 ± 0.021 ns/op
> Single.storeStore avgt3 0.410 ± 0.061 ns/op
>
> # -XX:DisableIntrinsic=_fullFence,_loadFence
> Single.acquire avgt3 15.822 ± 0.282 ns/op <--- upgraded, calls
> runtime
> Single.fullavgt3 15.851 ± 0.127 ns/op <--- calls runtime
> Single.loadLoadavgt3 15.829 ± 0.045 ns/op <--- upgraded, calls
> runtime
> Single.plain avgt3 0.406 ± 0.001 ns/op
> Single.release avgt3 0.414 ± 0.156 ns/op
> Single.storeStore avgt3 0.422 ± 0.452 ns/op
>
> # -XX:DisableIntrinsic=_fullFence,_storeFence
> Single.acquire avgt3 0.407 ± 0.016 ns/op
> Single.fullavgt3 15.347 ± 6.783 ns/op <--- calls runtime
> Single.loadLoadavgt3 0.406 ± 0.001 ns/op
> Single.plain avgt3 0.406 ± 0.002 ns/op
> Single.release avgt3 15.828 ± 0.019 ns/op <--- upgraded, calls
> runtime
> Single.storeStore avgt3 15.834 ± 0.045 ns/op <--- upgraded, calls
> runtime
>
> # -XX:DisableIntrinsic=_fullFence,_loadFence,_storeFence
> Single.acquire avgt3 15.838 ± 0.030 ns/op <--- upgraded, calls
> runtime
> Single.fullavgt3 15.854 ± 0.277 ns/op <--- calls runtime
> Single.loadLoadavgt3 15.826 ± 0.160 ns/op <--- upgraded, calls
> runtime
> Single.plain avgt3 0.406 ± 0.003 ns/op
> Single.release avgt3 15.838 ± 0.019 ns/op <--- upgraded, calls
> runtime
> Single.storeStore avgt3 15.844 ± 0.104 ns/op <--- upgraded, calls
> runtime
>
>
> Additional testing:
> - [x] Linux x86_64 fastdebug `tier1`
Aleksey Shipilev has updated the pull request incrementally with one additional
commit since the last revision:
Restore RN for fullFence
-
Changes:
- all: https://git.openjdk.java.net/jdk/pull/6149/files
- new: https://git.openjdk.java.net/jdk/pull/6149/files/e2c623be..a0fd03ee
Webrevs:
- full: https://webrevs.openjdk.java.net/?repo=jdk=6149=01
- incr: https://webrevs.openjdk.java.net/?repo=jdk=6149=00-01
Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
Patch: https://git.openjdk.java.net/jdk/pull/6149.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/6149/head:pull/6149
PR: https://git.openjdk.java.net/jdk/pull/6149
