[PW_SID:1001709] Improve roam scan strategy #481
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This is taken care of by the individual cache items and if none exist, tar fails.
Return the number of freqs in a scan_freq_set, useful for knowing how big the set is.
Splits the scan frequencies into more subsets that have been ordered such that the more common frequencies appear first, and the more uncommon frequencies last. Non-DFS channels are also added to the earlier subsets to prioritize fast-scanning frequencies. This approach allows iwd to scan the frequencies with the statistically highest chance for BSSes first, resulting in shorter scan times until a good BSS is found. In future patches this will also be used when roaming.
When iwd decides to roam, it scans either neighbor freqs or known freqs (if neighbors are not available). If it fails to roam after getting the scan results, it scans ALL freqs. There's a high chance that both neighbor and/or known scans fail to roam and we end up scanning all freqs. This is very slow and if you're already moving away from the current BSS, there's a high chance you will lose connection completely before the scan is finished. Instead of scanning all freqs at once, use the already-defined subsets to optimize the scans. The subsets contain a handful of freqs each and are ordered to increase the chance of finding a good BSS early. In order to not scan the same freq multiple times, use a list (scanned_freqs) to keep track of which freqs have been scanned in the current roam attempt. When a roam scan is triggered, add the most prioritized freqs to the list of freqs that should be scanned. The order of priority is: 1. Neighbor freqs 2. Known freqs 3. Subsets, starting with index 0 and incrementing if the subset is exhausted A freq is only added to the scan if it has not yet been scanned in the current roam attempt. An exception to this are neighbor freqs. They have a higher chance of containing good BSSes, so they're scanned every 3rd scan (defined by STATION_SCANS_BEFORE_NEIGHBOR_SCAN). This approach results in more scans, but fewer freqs per scan, leading to shorter delays between scan results. It also avoids scanning the same freqs back-to-back, which is generally not very useful. In combination with the subset ordering, this increases the chance of finding a good BSS early and results in better roaming performance.
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Fetch PR Prep - Setup ELL Make Distcheck Build - Configure Make Check Output: Make Check w/Valgrind Output: Incremental Build with patches Output: |
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Fetch PR GitLint Prep - Setup ELL Make Distcheck Build - Configure Make Check Output: Make Check w/Valgrind Output: Incremental Build with patches Output: Autotest Runner Output: Clang Build Output: |
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Return the number of freqs in a scan_freq_set, useful for knowing how
big the set is.
src/util.c | 11 +++++++++++
src/util.h | 1 +
2 files changed, 12 insertions(+)