Stefan Fuhrmann wrote: > Julian Foad wrote: >>> URL:http://svn.apache.org/viewvc?rev=1333326&view=rev >>> Introduce private API functions that wrap apr_hash_make_custom >>> and return hash tables that are 2 to 4 times faster than the >>> APR default. >> >> Would it be sensible to propose these (the hash-functions) for >> inclusion in APR itself? > > Certainly. The question would be whether Apache is > meant to run on CPUs without a decent MUL.
I don't understand why that question is relevant. >> I suggest changing the names to >> >> svn_hash__make_compatible >> svn_hash__make # faster than the 'compatible' one >> >> [...] > > The "fast" variant had a potential page overflow (segfault). > Fixing that issue would have made it slower than the > compatible version for the APR_HASH_KEY_STRING case. > Because the latter constitutes the vast majority of uses > within SVN, I remove the *_fast code in r1340590. Great, it's better to just have one version. >>> Modified: subversion/trunk/subversion/libsvn_subr/hash.c >>> URL:http://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_subr/hash.c?rev=1333326&r1=1333325&r2=1333326&view=diff >>> ============================================================================== >>> --- subversion/trunk/subversion/libsvn_subr/hash.c (original) >>> +++ subversion/trunk/subversion/libsvn_subr/hash.c Thu May 3 07:16:11 2012 >>> +/*** Optimized hash functions ***/ >>> + >>> +/* Optimized version of apr_hashfunc_default. It assumes that the CPU has >>> + * 32-bit multiplications with high throughput of at least 1 operation >>> + * every 3 cycles. Latency is not an issue. Another optimization is a >>> + * mildly unrolled main loop. >> >> Such specific details should at least refer to a specific version >> of apr_hashfunc_default(). Perhaps also (for the "1 op per 3 cycles" >> part, in particular) a specific system architecture or compiler. > > r1340601 explains why that is a reasonable assumption. What's missing is a statement that this is an optimized version of "apr_hashfunc_default in APR 1.4.5". - Julian
