Sorry for this stupid question. A very simple/short MPI program runs on a 4 core desktop computer. I would expect the Speed-up to drop after 8 (HT) threads, but it continues almost in a straight line until 128 threads (the default system limit). How is this possible? Thanks.
if there are not much communication between cores,
【在 r***e 的大作中提到】 : Sorry for this stupid question. : A very simple/short MPI program runs on a 4 core : desktop computer. I would expect the Speed-up to : drop after 8 (HT) threads, but it continues almost : in a straight line until 128 threads (the default : system limit). : How is this possible? Thanks.
I still don't get it. On a 4 core i7 processor with 8 hyper-threads, say for an embarrassingly parallel problem the sequential time is 1024 seconds then 2 cores will take 512 seconds each, S = 2; 4 cores will take 256 seconds each, s = 4; 8 cores will take 128 seconds each, s = 8; 16 cores will take 64 seconds each, however, as 8 have to wait, it still takes 64+64 = 128 seconds, s = 8; 32 cores, s = 8; But what I am getting is this:
【在 j**u 的大作中提到】 : if there are not much communication between cores,
【在 r***e 的大作中提到】 : : I still don't get it. : On a 4 core i7 processor with 8 hyper-threads, : say for an embarrassingly parallel problem : the sequential time is 1024 seconds : then 2 cores will take 512 seconds each, S = 2; : 4 cores will take 256 seconds each, s = 4; : 8 cores will take 128 seconds each, s = 8; : 16 cores will take 64 seconds each, : however, as 8 have to wait,
Old bear, may I bother you with another naïve question? I tried to isolate a problem, so I wrote this short program to test basic send and receive. http://pastebin.com/CMp63hkK It works as expected on one computer Fedora 22 with OpenMPI, but "always" hangs on another computer with Fedora 22 with MPICH. I tested them on localhost only in both cases, same gcc version. If I use reduce or if I avoid send/receive same node (0), then it works. Is it a rule that I can't send/receive the same node (0), or is there a mistake in my code? Thank you!
m*u
40 楼
珍稀动物的证书上说了weight是 27 g
【在 h****7 的大作中提到】 : 上面纯度是0.900,下面是0.925
x*x
41 楼
MPI_Send has blocking semantics. It may or may not block depending on the MPI implementation.Both OpenMPI and MPICH behaved correctly.The problem is with the program. The correct way is to use MPI_Isend instead.
【在 r***e 的大作中提到】 : Old bear, may I bother you with another naïve question? : I tried to isolate a problem, so I wrote this short program to : test basic send and receive. : http://pastebin.com/CMp63hkK : It works as expected on one computer Fedora 22 with OpenMPI, : but "always" hangs on another computer with Fedora 22 with MPICH. : I tested them on localhost only in both cases, same gcc version. : If I use reduce or if I avoid send/receive same node (0), : then it works. : Is it a rule that I can't send/receive the same node (0),
h*7
42 楼
对,我买的30克80年奥林匹克没有证书。
r*e
43 楼
谢谢!
【在 x*x 的大作中提到】 : MPI_Send has blocking semantics. It may or may not block depending on the : MPI implementation.Both OpenMPI and MPICH behaved correctly.The problem is : with the program. : The correct way is to use MPI_Isend instead.