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service: reduce average case service core overhead

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Optimize service loop so that the starting point is the lowest-indexed
service mapped to the lcore in question, and terminate the loop at the
highest-indexed service.

While the worst case latency remains the same, this patch
significantly reduces the service framework overhead for the average
case. In particular, scenarios where an lcore only runs a single
service, or multiple services which id values are close (e.g., three
services with ids 17, 18 and 22), show significant improvements.

The worse case is a where the lcore two services mapped to it; one
with service id 0 and the other with id 63.

On a service lcore serving a single service, the service loop overhead
is reduced from ~190 core clock cycles to ~46, on an Intel Cascade
Lake generation Xeon. On weakly ordered CPUs, the gain is larger,
since the loop included load-acquire atomic operations.

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>
This commit is contained in:
Mattias Rönnblom 2022-10-05 11:16:12 +02:00 committed by David Marchand
parent b54ade8f24
commit 074b4db247
1 changed files with 15 additions and 4 deletions
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19
lib/eal/common/rte_service.c
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@ -78,6 +78,11 @@ static uint32_t rte_service_library_initialized;
int32_t
rte_service_init(void)
{
/* Hard limit due to the use of an uint64_t-based bitmask (and the
* clzl intrinsic).
*/
RTE_BUILD_BUG_ON(RTE_SERVICE_NUM_MAX > 64);
if (rte_service_library_initialized) {
RTE_LOG(NOTICE, EAL,
"service library init() called, init flag %d\n",
@ -470,7 +475,6 @@ static int32_t
service_runner_func(void *arg)
{
RTE_SET_USED(arg);
uint32_t i;
const int lcore = rte_lcore_id();
struct core_state *cs = &lcore_states[lcore];
@ -484,10 +488,17 @@ service_runner_func(void *arg)
RUNSTATE_RUNNING) {
const uint64_t service_mask = cs->service_mask;
uint8_t start_id;
uint8_t end_id;
uint8_t i;
for (i = 0; i < RTE_SERVICE_NUM_MAX; i++) {
if (!service_registered(i))
continue;
if (service_mask == 0)
continue;
start_id = __builtin_ctzl(service_mask);
end_id = 64 - __builtin_clzl(service_mask);
for (i = start_id; i < end_id; i++) {
/* return value ignored as no change to code flow */
service_run(i, cs, service_mask, service_get(i), 1);
}