Herbert Xu a écrit :
Andrew Morton <[EMAIL PROTECTED]> wrote:
It is possible to introduce UDP packet losses by reading
the proc file entry /proc/net/tcp. The really strange thing is that
the error counters for packet drops are not increased.
Please try this patch and let us know if it helps.
[TCPv4]: Improve BH latency in /proc/net/tcp
Currently the code for /proc/net/tcp disable BH while iterating
over the entire established hash table. Even though we call
cond_resched_softirq for each entry, we still won't process
softirq's as regularly as we would otherwise do which results
in poor performance when the system is loaded near capacity.
This anomaly comes from the 2.4 code where this was all in a
single function and the local_bh_disable might have made sense
as a small optimisation.
The cost of each local_bh_disable is so small when compared
against the increased latency in keeping it disabled over a
large but mostly empty TCP established hash table that we
should just move it to the individual read_lock/read_unlock
calls as we do in inet_diag.
But its not really true : cond_resched_softirq() is called for
each bucket in hash table, empty or not.
If this patch really helps, this means cond_resched_softirq()
doesnt work at all and should be fixed, or just zapped as it
is seldom used.
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