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author | David S. Miller <davem@davemloft.net> | 2010-12-26 22:37:05 -0800 |
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committer | David S. Miller <davem@davemloft.net> | 2010-12-26 22:37:05 -0800 |
commit | 17f7f4d9fcce8f1b75b5f735569309dee7665968 (patch) | |
tree | 14d7e49ca0053a0fcab3c33b5023bf3f90c5c08a /include/linux/cnt32_to_63.h | |
parent | 041110a439e21cd40709ead4ffbfa8034619ad77 (diff) | |
parent | d7c1255a3a21e98bdc64df8ccf005a174d7e6289 (diff) |
Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6
Conflicts:
net/ipv4/fib_frontend.c
Diffstat (limited to 'include/linux/cnt32_to_63.h')
-rw-r--r-- | include/linux/cnt32_to_63.h | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/include/linux/cnt32_to_63.h b/include/linux/cnt32_to_63.h index 7605fdd1eb6..e3d8bf26e5e 100644 --- a/include/linux/cnt32_to_63.h +++ b/include/linux/cnt32_to_63.h @@ -61,13 +61,31 @@ union cnt32_to_63 { * * 2) this code must not be preempted for a duration longer than the * 32-bit counter half period minus the longest period between two - * calls to this code. + * calls to this code; * * Those requirements ensure proper update to the state bit in memory. * This is usually not a problem in practice, but if it is then a kernel * timer should be scheduled to manage for this code to be executed often * enough. * + * And finally: + * + * 3) the cnt_lo argument must be seen as a globally incrementing value, + * meaning that it should be a direct reference to the counter data which + * can be evaluated according to a specific ordering within the macro, + * and not the result of a previous evaluation stored in a variable. + * + * For example, this is wrong: + * + * u32 partial = get_hw_count(); + * u64 full = cnt32_to_63(partial); + * return full; + * + * This is fine: + * + * u64 full = cnt32_to_63(get_hw_count()); + * return full; + * * Note that the top bit (bit 63) in the returned value should be considered * as garbage. It is not cleared here because callers are likely to use a * multiplier on the returned value which can get rid of the top bit |