> From: Bruce Richardson [mailto:bruce.richard...@intel.com] > Sent: Wednesday, 26 February 2025 17.53 > > On Wed, Feb 26, 2025 at 03:59:22PM +0000, Morten Brørup wrote: > > The comparisons lcore_id < RTE_MAX_LCORE and lcore_id != LCORE_ID_ANY > are > > equivalent, but the latter compiles to fewer bytes of code space. > > Similarly for lcore_id >= RTE_MAX_LCORE and lcore_id == LCORE_ID_ANY. > > > > The rte_mempool_get_ops() function is also used in the fast path, so > > RTE_VERIFY() was replaced by RTE_ASSERT(). > > > > Compilers implicitly consider comparisons of variable == 0 likely, so > > unlikely() was added to the check for no mempool cache (mp- > >cache_size == > > 0) in the rte_mempool_default_cache() function. > > > > The rte_mempool_do_generic_put() function for adding objects to a > mempool > > was refactored as follows: > > - The comparison for the request itself being too big, which is > considered > > unlikely, was moved down and out of the code path where the cache > has > > sufficient room for the added objects, which is considered the most > > likely code path. > > - Added __rte_assume() about the cache length, size and threshold, > for > > compiler optimization when "n" is compile time constant. > > - Added __rte_assume() about "ret" being zero, so other functions > using > > the value returned by this function can be potentially optimized by > the > > compiler; especially when it merges multiple sequential code paths > of > > inlined code depending on the return value being either zero or > > negative. > > - The refactored source code (with comments) made the separate > comment > > describing the cache flush/add algorithm superfluous, so it was > removed. > > > > A few more likely()/unlikely() were added. > > > > A few comments were improved for readability. > > > > Some assertions, RTE_ASSERT(), were added. Most importantly to assert > that > > the return values of the mempool drivers' enqueue and dequeue > operations > > are API compliant, i.e. 0 (for success) or negative (for failure), > and > > never positive. > > > > Signed-off-by: Morten Brørup <m...@smartsharesystems.com> > > --- > > lib/mempool/rte_mempool.h | 67 ++++++++++++++++++++++--------------- > -- > > 1 file changed, 38 insertions(+), 29 deletions(-) > > > Is there any measurable performance change with these modifications?
It varies. Here are some of the good ones, tested on a VM under VMware: mempool_autotest cache=512 cores=1 n_get_bulk=64 n_put_bulk=64 n_keep=128 constant_n=0 rate_persec=1309408130 -> 1417067889 : +8.2 % mempool_autotest cache=512 cores=1 n_get_bulk=64 n_put_bulk=64 n_keep=128 constant_n=1 rate_persec=1479812844 -> 1573307159 : +6.3 % mempool_autotest cache=512 cores=1 n_max_bulk=32 n_keep=128 constant_n=0 rate_persec=825183959 -> 868013386 : +5.2 % The last result is from a new type of test where the size of every get/put varies between 1 and n_max_bulk, so the CPU's dynamic branch predictor cannot predict the request size. I'll probably provide a separate patch for test_mempool_perf.c with this new test type, when I have finished it.
