[Sbcl-devel] GC time and multiple threads

[David L. <da...@li...>]

Hi,

is garbage collection time in SBCL dependent on the total number of
threads started?  In GC-intensive code, I noticed that a large amount of
real time was spent when background threads were present, while run time
as measured by get-internal-run-time seemed much lower.

Attached is a small test function which starts N threads, then allocates
data in the initial thread.  The background threads just call SLEEP.

I get the following results for current SBCL (0.8.10.48 with sb-futex):

$ sbcl --noinform --userinit /dev/null --load test.cl --eval '(test n)' --eval '(quit)'

Times for 0 <= N <= 4 (with GC enabled):
5s real time, 4232 int. real time, 3937 int. run time
10s real time, 10141 int. real time, 3934 int. run time
18s real time, 17135 int. real time, 3946 int. run time
23s real time, 22997 int. real time, 3941 int. run time
28s real time, 27999 int. real time, 3949 int. run time

Times for 0 <= N <= 7 (with sb-sys:without-gcing):
1s real time, 1527 int. real time, 1409 int. run time
2s real time, 1519 int. real time, 1408 int. run time
2s real time, 1515 int. real time, 1409 int. run time
4s real time, 4524 int. real time, 1407 int. run time
1s real time, 1509 int. real time, 1409 int. run time
1s real time, 1503 int. real time, 1409 int. run time
2s real time, 1512 int. real time, 1412 int. run time
1s real time, 1522 int. real time, 1410 int. run time



Thanks,
David