+CC: Fidaullah Noonari <fidaullah.noon...@emumba.com>, your name also shows up in the git log; perhaps you can help review this patch.
> From: Thomas Monjalon [mailto:tho...@monjalon.net] > Sent: Wednesday, 15 February 2023 11.10 > > Looking for reviewers please. > > 10/02/2023 07:30, Fengnan Chang: > > Here is a simple test case: > > " > > uint64_t entry_time, time; > > size_t size = 4096; > > unsigned align = 4096; > > for (int j = 0; j < 10; j++) { > > entry_time = rte_get_timer_cycles(); > > for (int i = 0; i < 2000; i++) { > > rte_malloc(NULL, size, align); > > } > > time = (rte_get_timer_cycles()-entry_time) * 1000000 / > > rte_get_timer_hz(); > > printf("total open time %lu avg time %lu\n", time, time/2000); > > } > > " > > > > Single rte_malloc cost time may becomes wrose as the number of malloc > > increases, In my env, first round avg time is 15us, second is 44us, > > third is 77us, fourth is 168us... > > > > The reason is,in the malloc process, malloc_elem_alloc may split > new_elem > > if there have too much free space after new_elem, and insert the > trailer > > into freelist. When alloc 4k with align 4k, the trailer very likely > insert > > to free_head[2] again, it makes free_head[2] longer. when alloc 4k > again, > > it will search free_head[2] from begin, with the number of malloc > increases, > > search free_head[2] need more time, so the performance will become > worse. > > Same problem will also occurs in alloc 64k with align 64k, but if > alloc > > 4k with align 64, doesn't have this problem. > > > > Fix this by adjust free_head list size range, make free_head[3] hold > > elements which bigger or equal 4k, free_head[4] hold elements which > bigger > > or equal 16k. > > In terms of probabilities, when alloc 4k or 16k, the probability of > finding > > a suitable elem from a larger size list is greater than from a > smaller > > size list. > > > > Signed-off-by: Fengnan Chang <changfeng...@bytedance.com> > > --- > > lib/eal/common/malloc_elem.c | 14 +++++++------- > > 1 file changed, 7 insertions(+), 7 deletions(-) > > > > diff --git a/lib/eal/common/malloc_elem.c > b/lib/eal/common/malloc_elem.c > > index 83f05497cc..35a2313d04 100644 > > --- a/lib/eal/common/malloc_elem.c > > +++ b/lib/eal/common/malloc_elem.c > > @@ -367,11 +367,11 @@ prev_elem_is_adjacent(struct malloc_elem *elem) > > * containing larger elements. > > * > > * Example element size ranges for a heap with five free lists: > > - * heap->free_head[0] - (0 , 2^8] > > - * heap->free_head[1] - (2^8 , 2^10] > > - * heap->free_head[2] - (2^10 ,2^12] > > - * heap->free_head[3] - (2^12, 2^14] > > - * heap->free_head[4] - (2^14, MAX_SIZE] > > + * heap->free_head[0] - (0 , 2^8) > > + * heap->free_head[1] - [2^8 , 2^10) > > + * heap->free_head[2] - [2^10 ,2^12) > > + * heap->free_head[3] - [2^12, 2^14) > > + * heap->free_head[4] - [2^14, MAX_SIZE] > > */ > > size_t > > malloc_elem_free_list_index(size_t size) > > @@ -385,8 +385,8 @@ malloc_elem_free_list_index(size_t size) > > if (size <= (1UL << MALLOC_MINSIZE_LOG2)) > > return 0; > > > > - /* Find next power of 2 >= size. */ > > - log2 = sizeof(size) * 8 - __builtin_clzl(size - 1); > > + /* Find next power of 2 > size. */ > > + log2 = sizeof(size) * 8 - __builtin_clzl(size); > > > > /* Compute freelist index, based on log2(size). */ > > index = (log2 - MALLOC_MINSIZE_LOG2 + MALLOC_LOG2_INCREMENT - 1) > / > > I gave up reviewing in depth, because the existing code is not easy to quickly understand, and it would take too long for me. E.g. the malloc_elem->size is field is undocumented, and find_suitable_element() calls the malloc_elem_free_list_index() function with the raw size (as passed to the function), but malloc_elem_free_list_insert() calls the malloc_elem_free_list_index() with malloc_elem->size - MALLOC_ELEM_HEADER_LEN. Looking isolated at the patch itself... I agree with the way the patch modifies the ranges of the free list, and the consequential removal of the "- 1" from the calculation of log2. Intuitively, the lists should cover ranges such as [0x100..0x3FF], which this patch does, not [0x101..0x400], how it was previously... The ranges with this patch make much more sense. So if the existing code is otherwise correct, i.e. handles the size with/without MALLOC_ELEM_HEADER_LEN correctly, my gut feeling says this patch is an improvement. Acked-by: Morten Brørup <m...@smartsharesystems.com>
