mirror of
https://github.com/haproxy/haproxy.git
synced 2026-04-15 21:59:41 -04:00
9dd56da730
It was noticed in haproxy that in certain extreme cases, a write lock subject to EBO may fail for a very long time in front of a large set of readers constantly trying to upgrade to the S state. The reason is that among many readers, one will succeed in its upgrade, and this situation can last for a very long time with many readers upgrading in turn, while the writer waits longer and longer before trying again. Here we're taking a reasonable approach which is that the write lock should have a higher precedence in its attempt to grab the lock. What is done is that instead of fully rolling back in case of conflict with a pure S lock, the writer will only release its read part in order to let the S upgrade to W if needed, and finish its operations. This guarantees no other seek/read/write can enter. Once the conflict is resolved, the writer grabs the read part again and waits for readers to be gone (in practice it could even return without waiting since we know that any possible wanderers would leave or even not be there at all, but it avoids a complicated loop code that wouldn't improve the practical situation but inflate the code). Thanks to this change, the maximum write lock latency on a 48 threads AMD with aheavily loaded scheduler went down from 256 to 64 ms, and the number of occurrences of 32ms or more was divided by 300, while all occurrences of 1ms or less were multiplied by up to 3 (3 for the 4-16ns cases). This is plock commit b6a28366d156812f59c91346edc2eab6374a5ebd. |
||
|---|---|---|
| .. | ||
| atomic-ops.h | ||
| cebtree-prv.h | ||
| cebtree.h | ||
| cebu32_tree.h | ||
| cebu64_tree.h | ||
| cebua_tree.h | ||
| cebub_tree.h | ||
| cebuib_tree.h | ||
| cebuis_tree.h | ||
| cebul_tree.h | ||
| cebus_tree.h | ||
| eb32sctree.h | ||
| eb32tree.h | ||
| eb64tree.h | ||
| ebimtree.h | ||
| ebistree.h | ||
| ebmbtree.h | ||
| ebpttree.h | ||
| ebsttree.h | ||
| ebtree-t.h | ||
| ebtree.h | ||
| ist.h | ||
| lru.h | ||
| mjson.h | ||
| mt_list.h | ||
| plock.h | ||
| sha1.h | ||
| slz-tables.h | ||
| slz.h | ||
| xxhash.h | ||