On Thu, May 23, 2013 at 2:01 AM, Blair Zajac <bl...@orcaware.com> wrote:
> On 05/22/2013 04:22 PM, stef...@apache.org wrote: > >> Author: stefan2 >> Date: Wed May 22 23:22:22 2013 >> New Revision: 1485499 >> >> URL: http://svn.apache.org/r1485499 >> Log: >> Reduce ra_svn protocol parsing overhead. >> >> * subversion/libsvn_ra_svn/**marshal.c >> (vparse_tuple): test for the most frequent item types first >> >> Modified: >> subversion/trunk/subversion/**libsvn_ra_svn/marshal.c >> >> Modified: subversion/trunk/subversion/**libsvn_ra_svn/marshal.c >> URL: http://svn.apache.org/viewvc/**subversion/trunk/subversion/** >> libsvn_ra_svn/marshal.c?rev=**1485499&r1=1485498&r2=1485499&**view=diff<http://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_ra_svn/marshal.c?rev=1485499&r1=1485498&r2=1485499&view=diff> >> ==============================**==============================** >> ================== >> --- subversion/trunk/subversion/**libsvn_ra_svn/marshal.c (original) >> +++ subversion/trunk/subversion/**libsvn_ra_svn/marshal.c Wed May 22 >> 23:22:22 2013 >> @@ -1202,14 +1202,15 @@ static svn_error_t *vparse_tuple(const a >> if (**fmt == '?') >> (*fmt)++; >> elt = &APR_ARRAY_IDX(items, count, svn_ra_svn_item_t); >> - if (**fmt == 'n' && elt->kind == SVN_RA_SVN_NUMBER) >> - *va_arg(*ap, apr_uint64_t *) = elt->u.number; >> - else if (**fmt == 'r' && elt->kind == SVN_RA_SVN_NUMBER) >> - *va_arg(*ap, svn_revnum_t *) = (svn_revnum_t) elt->u.number; >> - else if (**fmt == 's' && elt->kind == SVN_RA_SVN_STRING) >> - *va_arg(*ap, svn_string_t **) = elt->u.string; >> + if (**fmt == '(' && elt->kind == SVN_RA_SVN_LIST) >> + { >> + (*fmt)++; >> + SVN_ERR(vparse_tuple(elt->u.**list, pool, fmt, ap)); >> + } >> > > Out of curiosity, how much cost is there in the double dereferencing of > fmt? Don't know but since there are no intermittent writes, **fmt can be read once and then be taken from the same register over and over again. The performance relevant part are the branch misprediction rates. We see about 1 .. 1.5 mispredicted jumps / iteration. > Could you save it in a local variable and do the if/else on that instead? The compiler already does that. > Also, would a switch block be more efficient? > Possibly. *If* the compiler generated a jump table for it, we might reduce the misprediction rate by 50% or so. But my strategy is rather to replace the usage of vparse_tuple by a set of functions that extract the data explicitly - similar to what the command functions already do. -- Stefan^2. -- *Join one of our free daily demo sessions on* *Scaling Subversion for the Enterprise <http://www.wandisco.com/training/webinars>* * *
