net/smc: Fix pos miscalculation in statistics
[ Upstream commit a950a592 ] SMC_STAT_PAYLOAD_SUB(_smc_stats, _tech, key, _len, _rc) will calculate wrong bucket positions for payloads of exactly 4096 bytes and (1 << (m + 12)) bytes, with m == SMC_BUF_MAX - 1. Intended bucket distribution: Assume l == size of payload, m == SMC_BUF_MAX - 1. Bucket 0 : 0 < l <= 2^13 Bucket n, 1 <= n <= m-1 : 2^(n+12) < l <= 2^(n+13) Bucket m : l > 2^(m+12) Current solution: _pos = fls64((l) >> 13) [...] _pos = (_pos < m) ? ((l == 1 << (_pos + 12)) ? _pos - 1 : _pos) : m For l == 4096, _pos == -1, but should be _pos == 0. For l == (1 << (m + 12)), _pos == m, but should be _pos == m - 1. In order to avoid special treatment of these corner cases, the calculation is adjusted. The new solution first subtracts the length by one, and then calculates the correct bucket by shifting accordingly, i.e. _pos = fls64((l - 1) >> 13), l > 0. This not only fixes the issues named above, but also makes the whole bucket assignment easier to follow. Same is done for SMC_STAT_RMB_SIZE_SUB(_smc_stats, _tech, k, _len), where the calculation of the bucket position is similar to the one named above. Fixes: e0e4b8fa ("net/smc: Add SMC statistics support") Suggested-by:Halil Pasic <pasic@linux.ibm.com> Signed-off-by:
Nils Hoppmann <niho@linux.ibm.com> Reviewed-by:
Halil Pasic <pasic@linux.ibm.com> Reviewed-by:
Wenjia Zhang <wenjia@linux.ibm.com> Reviewed-by:
Dust Li <dust.li@linux.alibaba.com> Signed-off-by:
David S. Miller <davem@davemloft.net> Signed-off-by:
Sasha Levin <sashal@kernel.org>
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e4f2611f
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