Reset TLH sizing at first increment for CS #7251
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We reduce current refresh size at GC points, so that slow allocating threads have a chance to reduce their current refresh size. It's done toward the end of a GC cycle, which means that for Concurrent Scavegner it's done at the end of 2nd GC increment. However, it's slighty better to do it at the end of 1st increment since it will cuase TLH to be slighly smaller during concurrent phase of the cycle. During the concurrent phase there are other activities like GC background threads and read-barriers that effectively slow down the allocation rate of mutator threads, so there is less contention among them and less need for larger TLHs. Also, since allocate space is much smaller during concurrent phase of GC, smaller TLHs will lead to smaller discards for the last TLH refresh, which leads to more tilting and less frequent GC cycles. Signed-off-by: Aleksandar Micic <Aleksandar_Micic@ca.ibm.com>
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In an experiment, with all other things equal this change led to more tilting and lower number of GC cycles: before: |
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@dmitripivkine please, review |
dmitripivkine
approved these changes
Feb 7, 2024
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@babsingh Would you please to help to merge this? |
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jenkins build all |
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Existing testing is sufficient. riscv failed due to an infra issue, and OSX failed due to a known and unrelated issue: #7181. |
babsingh
approved these changes
Feb 7, 2024
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We reduce current refresh size at GC points, so that slow allocating threads have a chance to reduce their current refresh size.
It's done toward the end of a GC cycle, which means that for Concurrent Scavegner it's done at the end of 2nd GC increment.
However, it's slighty better to do it at the end of 1st increment since it will cause TLH to be slighly smaller during concurrent phase of the cycle.
During the concurrent phase there are other activities like GC background threads and read-barriers that effectively slow down the allocation rate of mutator threads, so there is less contention among them and less need for larger TLHs.
Also, since allocate space is much smaller during concurrent phase of GC, smaller TLHs will lead to smaller discards for the last TLH refresh, which leads to more tilting and less frequent GC cycles.