fix: collect eth stats under the mutex #113
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DPDK's interface for collecting device statistics is not thread-safe. However, we can easily achieve a situation when multiple threads try to collect stats for its purposes, because, for example, we spawn a separate thread for each CP-DP connection. Such thread-unsafety results in device statistics skewness, and maybe other more serious bugs. Things get even worse if we try to trace the call graph from DPDK to the drivers. For example, both `rte_eth_stats_get` and `rte_eth_xstats_get` are end with calling `ice_stats_get` for ICE driver, which is also not thread-safe. As we have these calls scattered across the entire dataplane - some of them under the "global" mutex, some are not - we have two possible ways how to solve the issue above. The first one is to protect all branches under the same mutex, but it makes the code even harder to understand. Mutext hell. The second one - is to serialize API calls, making them execute in a single thread, this is better, but requires massive code refactoring. This PR follows the first way. Add the mutex. Pray to not be caught by deadlocks.
3Hren
commented
Feb 6, 2024
| for (const auto& [portId, port] : dataPlane->ports) | ||
| { | ||
| (void)port; | ||
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| rte_eth_stats stats; | ||
| memset(&stats, 0, sizeof(stats)); |
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This is no longer needed, since DPDK zeroes stats for us.
taitov
approved these changes
Feb 6, 2024
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DPDK's interface for collecting device statistics is not thread-safe. However, we can easily achieve a situation when multiple threads try to collect stats for its purposes, because, for example, we spawn a separate thread for each CP-DP connection. Such thread-unsafety results in device statistics skewness, and maybe other more serious bugs. Things get even worse if we try to trace the call graph from DPDK to the drivers.
For example, both
rte_eth_stats_getandrte_eth_xstats_getare end with callingice_stats_getfor ICE driver, which is also not thread-safe.As we have these calls scattered across the entire dataplane - some of them under the "global" mutex, some are not - we have two possible ways how to solve the issue above. The first one is to protect all branches under the same mutex, but it makes the code even harder to understand. Mutext hell. The second one - is to serialize API calls, making them execute in a single thread, this is better, but requires massive code refactoring.
This PR follows the first way. Add the mutex. Pray to not be caught by deadlocks.