[PATCH v3 0/3] thread-pool: fix performance regression

[Paolo Bonzini <pbonzini@redhat.com>]

Together, these two patches fix the performance regression induced by
QemuSemaphore; individually they don't though.

The third patch is a small cleanup on top, that was enabled by the
recent introduction of min_threads/max_threads knobs for the
thread pool.

6.2:
   iops        : min=58051, max=62260, avg=60282.57, stdev=1081.18, samples=30
    clat percentiles (usec):   1.00th=[  490],   99.99th=[  775]
   iops        : min=59401, max=61290, avg=60651.27, stdev=468.24, samples=30
    clat percentiles (usec):   1.00th=[  490],   99.99th=[  717]
   iops        : min=59583, max=60816, avg=60353.43, stdev=282.69, samples=30
    clat percentiles (usec):   1.00th=[  490],   99.99th=[  701]
   iops        : min=58099, max=60713, avg=59739.53, stdev=755.49, samples=30
    clat percentiles (usec):   1.00th=[  494],   99.99th=[  717]
	
patched:
   iops        : min=60616, max=62522, avg=61654.37, stdev=555.67, samples=30
    clat percentiles (usec):   1.00th=[  474],   99.99th=[ 1303]
   iops        : min=61841, max=63600, avg=62878.47, stdev=442.40, samples=30
    clat percentiles (usec):   1.00th=[  465],   99.99th=[  685]
   iops        : min=62976, max=63910, avg=63531.60, stdev=261.05, samples=30
    clat percentiles (usec):   1.00th=[  461],   99.99th=[  693]
   iops        : min=60803, max=63623, avg=62653.37, stdev=808.76, samples=30
    clat percentiles (usec):   1.00th=[  465],   99.99th=[  685]
	
Paolo

v1->v2: support min_threads/max_threads

v2->v3: fix NULL pointer dereference [Nicolas]

Paolo Bonzini (3):
  thread-pool: optimize scheduling of completion bottom half
  thread-pool: replace semaphore with condition variable
  thread-pool: remove stopping variable

 util/thread-pool.c | 74 +++++++++++++++++++---------------------------
 1 file changed, 30 insertions(+), 44 deletions(-)

-- 
2.36.0