sysctl net.inet.tcp.syncache.count
Robert Watson
rwatson at FreeBSD.org
Fri Nov 7 00:58:04 PST 2008
On Fri, 7 Nov 2008, Anton Yuzhaninov wrote:
> % sysctl net.inet.tcp.syncache
> net.inet.tcp.syncache.rst_on_sock_fail: 1
> net.inet.tcp.syncache.rexmtlimit: 3
> net.inet.tcp.syncache.hashsize: 1024
> net.inet.tcp.syncache.count: -84
> net.inet.tcp.syncache.cachelimit: 102400
> net.inet.tcp.syncache.bucketlimit: 100
>
> Why number of entries in syncache is negative?
The syncache entry is no longer protected by a single lock, since the locks on
the syncache are now per-hash bucket, so it looks like it's been corrupted.
This won't lead to other problems, as the count is updated as a statistic but
never used to, for example, enforce limits. We should probably eliminate the
statistic, since UMA already maintains the syncache entry count coherently as
part of its own statistics, along with other useful information:
robert at fledge:~> vmstat -z | head -1 ; vmstat -z | grep -i syncache
ITEM SIZE LIMIT USED FREE REQUESTS FAILURES
syncache: 104, 15392, 0, 222, 2638489, 0
I'm not convinced its worth adding the overhead of coherent statistics
gathering for the cache entry count if we already have it elsewhere.
Robert N M Watson
Computer Laboratory
University of Cambridge
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