[RFC PATCH v1 0/2] Fixed number of chromium workers

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

Hi Alviro,

Currently, a single chnet instance uses a single dedicated chromium
thread worker to perform an HTTP request. This doesn't scale well
because we need to spawn a new thread for each HTTP request.

Performing 4096 HTTP requests in parallel will spawn 4096 chromium
thread workers, which is too expensive and consuming too much
memory.

A single chromium thread worker can handle multiple HTTP requests.
This series creates a fixed number of chromium workers with ref
count to spread the jobs fairly across the chromium thread workers.

This greatly reduces the context switches and improve the performance.
It also greatly reduces the memory usage.

Implementation:

1) At initialization, when chnet_global_init() is called, create an
   array of pointers to `struct ch_thpool` and initialize those
   pointers to null. The number of elements in the array is
   taken from `std::thread::hardware_concurrency() - 1`.

2) When a new CHNet instance is created, its constructor calls
   `get_thread()` function which will initialize the array of
   pointers to `struct ch_thpool` if needed, then increment
   the ref count and it returns a pointer to the base::Thread
   class in `struct ch_thpool`.

3) When a CHNet instance is destroyed, it calls `put_thread()`
   function that will decrement the ref count of the
   `struct ch_thpool` and delete the object if the ref count
   reaches zero after getting decremented.


[ The implementation detail that fairly spread the job
  across multiple chromium threads worker is in get_thread()
  function, please have a look. ]

For the ring test case, the gained speedup is 33%.

Without this series:

  ammarfaizi2@integral2:~/work/ncns$ time taskset -c 0-7 make -j8 test -s
  Running /home/ammarfaizi2/work/ncns/tests/cpp/ring.t

  real    0m28.184s
  user    0m52.368s
  sys     0m27.582s


With this series:

  ammarfaizi2@integral2:~/work/ncns$ time taskset -c 0-7 make -j8 test -s
  Running /home/ammarfaizi2/work/ncns/tests/cpp/ring.t

  real    0m18.657s
  user    0m35.452s
  sys     0m2.146s

Please review and comment!

Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---

Ammar Faizi (2):
  chnet: Prepare global struct ch_thpool array
  chnet: Implement `get_thread()` and `put_thread()` function

 chnet/chnet.cc | 128 ++++++++++++++++++++++++++++++++++++++++++++++++-
 chnet/chnet.h  |   2 +-
 2 files changed, 128 insertions(+), 2 deletions(-)


base-commit: e1123a1e7b9526e4b12356bfed222386d4b00a80
-- 
Ammar Faizi