Re: [PATCH 0/3] *** timer library enhancements ***

On Aug 23, 2017, at 9:47 AM, Gabriel Carrillo [off-list ref] wrote:

In the current implementation of the DPDK timer library, timers can be
created and set to be handled by a target lcore by adding it to a
skiplist that corresponds to that lcore.  However, if an application
enables multiple lcores, and each of these lcores repeatedly attempts
to install timers on the same target lcore, overall application
throughput will be reduced as all lcores contend to acquire the lock
guarding the single skiplist of pending timers. 

This patchset addresses this scenario by adding an array of skiplists
to each lcore's priv_timer struct, such that when lcore i installs a
timer on lcore k, the timer will be added to the ith skiplist for
lcore k.  If lcore j installs a timer on lcore k simultaneously,
lcores i and j can both proceed since they will be acquiring different
locks for different lists. 

When lcore k processes its pending timers, it will traverse each skiplist
in its array and acquire a skiplist's lock while a run list is broken
out; meanwhile, all other lists can continue to be modified.  Then, all
run lists for lcore k are collected and traversed together so timers are
executed in their global order. 

What is the performance and/or latency added to the timeout now?

I worry about the case when just about all of the cores are enabled, which could be as high was 128 or more now.

One option is to have the lcore j that wants to install a timer on lcore k to pass a message via a ring to lcore k to add that timer. We could even add that logic into setting a timer on a different lcore then the caller in the current API. The ring would be a multi-producer and single consumer, we still have the lock. What am I missing here?

Gabriel Carrillo (3):
 timer: add per-installer pending lists for each lcore
 timer: handle timers installed from non-EAL threads
 doc: update timer lib docs

doc/guides/prog_guide/timer_lib.rst |  19 ++-
lib/librte_timer/rte_timer.c        | 329 +++++++++++++++++++++++-------------
lib/librte_timer/rte_timer.h        |   9 +-
3 files changed, 231 insertions(+), 126 deletions(-)

-- 
2.6.4

Regards,
Keith