Hi,
I have been writing CUDA kernels 5 years back and I liked a lot GPU computing. Now I work with CPUs and I have to apply the same techniques, even though CPUs have not the same architecture.
It is very hard to write macros with m4 and gcc, unroll loops and stuff like that, so I wonder if someone has already made some scripts or macros, or whatever code to apply the same principles of programming in CPU world ?
Thank you very much in advance
Nulik
I can’t really tell what you are looking for, but you might be interested in taking a look at the SPMD compiler which maps a CUDA-like programming model to the CPU: [url]https://ispc.github.io/[/url]. You may also want to take a look at OpenCL, for which CPU-based implementations exists (I think, I have not personally used one).
opencl, openmp, cilk plus to name a view. but cpus still differ from gpus, so the better you understand them the better code you can write. overall, gpus has much more raw power so once your algos can use it even at 10%, cpus aren’t a good replacement
That compiler is an interesting thing, thanks a lot of the info!
I will post some code so you could understand better:
void accept_connections(unsigned int num_conns) {
int fds[MAX_THREADS];
int conn_indexes[MAX_THREADS];
int conn_idx=0;
int new_bottom;
socklen_t slenghts[MAX_THREADS];
void *labels1[MAX_THREADS] = {&&a0,&&a1,&&a2,&&a3,&&a4,&&a5,&&a6,&&a7,&&a8,&&a9,&&a10,&&a11,&&a12,&&a13,&&a14,&&a15};
void *labels2[MAX_THREADS] = {&&b0,&&b1,&&b2,&&b3,&&b4,&&b5,&&b6,&&b7,&&b8,&&b9,&&b10,&&b11,&&b12,&&b13,&&b14,&&b15};
void *labels3[MAX_THREADS] = {&&c0,&&c1,&&c2,&&c3,&&c4,&&c5,&&c6,&&c7,&&c8,&&c9,&&c10,&&c11,&&c12,&&c13,&&c14,&&c15};
new_bottom=fl_conn_indexes_top-num_conns;
if (new_bottom<=0) return;
goto *labels1[num_conns];
a15:
conn_indexes[MAX_THREADS- 1]=fl_conn_indexes[fl_conn_indexes_top- 1];
a14:
conn_indexes[MAX_THREADS- 2]=fl_conn_indexes[fl_conn_indexes_top- 2];
a13:
conn_indexes[MAX_THREADS- 3]=fl_conn_indexes[fl_conn_indexes_top- 3];
a12:
conn_indexes[MAX_THREADS- 4]=fl_conn_indexes[fl_conn_indexes_top- 4];
a11:
conn_indexes[MAX_THREADS- 5]=fl_conn_indexes[fl_conn_indexes_top- 5];
a10:
conn_indexes[MAX_THREADS- 6]=fl_conn_indexes[fl_conn_indexes_top- 6];
a9:
conn_indexes[MAX_THREADS- 7]=fl_conn_indexes[fl_conn_indexes_top- 7];
a8:
conn_indexes[MAX_THREADS- 8]=fl_conn_indexes[fl_conn_indexes_top- 8];
a7:
conn_indexes[MAX_THREADS- 9]=fl_conn_indexes[fl_conn_indexes_top- 9];
a6:
conn_indexes[MAX_THREADS-10]=fl_conn_indexes[fl_conn_indexes_top-10];
a5:
conn_indexes[MAX_THREADS-11]=fl_conn_indexes[fl_conn_indexes_top-11];
a4:
conn_indexes[MAX_THREADS-12]=fl_conn_indexes[fl_conn_indexes_top-12];
a3:
conn_indexes[MAX_THREADS-13]=fl_conn_indexes[fl_conn_indexes_top-13];
a2:
conn_indexes[MAX_THREADS-14]=fl_conn_indexes[fl_conn_indexes_top-14];
a1:
conn_indexes[MAX_THREADS-15]=fl_conn_indexes[fl_conn_indexes_top-15];
a0:
conn_indexes[MAX_THREADS-16]=fl_conn_indexes[fl_conn_indexes_top-16];
fl_conn_indexes_top=fl_conn_indexes_top-num_conns;
goto *labels2[num_conns];
b15:
conn_fds[conn_indexes[MAX_THREADS- 1]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS- 1]],&slenghts[MAX_THREADS- 1]);
b14:
conn_fds[conn_indexes[MAX_THREADS- 2]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS- 2]],&slenghts[MAX_THREADS- 2]);
b13:
conn_fds[conn_indexes[MAX_THREADS- 3]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS- 3]],&slenghts[MAX_THREADS- 3]);
b12:
conn_fds[conn_indexes[MAX_THREADS- 4]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS- 4]],&slenghts[MAX_THREADS- 4]);
b11:
conn_fds[conn_indexes[MAX_THREADS- 5]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS- 5]],&slenghts[MAX_THREADS- 5]);
b10:
conn_fds[conn_indexes[MAX_THREADS- 6]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS- 6]],&slenghts[MAX_THREADS- 6]);
b9:
conn_fds[conn_indexes[MAX_THREADS- 7]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS- 7]],&slenghts[MAX_THREADS- 7]);
b8:
conn_fds[conn_indexes[MAX_THREADS- 8]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS- 8]],&slenghts[MAX_THREADS- 8]);
b7:
conn_fds[conn_indexes[MAX_THREADS- 9]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS- 9]],&slenghts[MAX_THREADS- 9]);
b6:
conn_fds[conn_indexes[MAX_THREADS-10]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS-10]],&slenghts[MAX_THREADS-10]);
b5:
conn_fds[conn_indexes[MAX_THREADS-11]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS-11]],&slenghts[MAX_THREADS-11]);
b4:
conn_fds[conn_indexes[MAX_THREADS-12]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS-12]],&slenghts[MAX_THREADS-12]);
b3:
conn_fds[conn_indexes[MAX_THREADS-13]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS-13]],&slenghts[MAX_THREADS-13]);
b2:
conn_fds[conn_indexes[MAX_THREADS-14]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS-14]],&slenghts[MAX_THREADS-14]);
b1:
conn_fds[conn_indexes[MAX_THREADS-15]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS-15]],&slenghts[MAX_THREADS-15]);
b0:
conn_fds[conn_indexes[MAX_THREADS-16]]=accept(nc_http_list.sock_fd,(struct sockaddr*) &conn_addresses[conn_indexes[MAX_THREADS-16]],&slenghts[MAX_THREADS-16]);
goto *labels3[num_conns];
c15:
conn_statuses[conn_indexes[MAX_THREADS- 1]]=CONN_STATUS_READING;
c14:
conn_statuses[conn_indexes[MAX_THREADS- 2]]=CONN_STATUS_READING;
c13:
conn_statuses[conn_indexes[MAX_THREADS- 3]]=CONN_STATUS_READING;
c12:
conn_statuses[conn_indexes[MAX_THREADS- 4]]=CONN_STATUS_READING;
c11:
conn_statuses[conn_indexes[MAX_THREADS- 5]]=CONN_STATUS_READING;
c10:
conn_statuses[conn_indexes[MAX_THREADS- 6]]=CONN_STATUS_READING;
c9:
conn_statuses[conn_indexes[MAX_THREADS- 7]]=CONN_STATUS_READING;
c8:
conn_statuses[conn_indexes[MAX_THREADS- 8]]=CONN_STATUS_READING;
c7:
conn_statuses[conn_indexes[MAX_THREADS- 9]]=CONN_STATUS_READING;
c6:
conn_statuses[conn_indexes[MAX_THREADS-10]]=CONN_STATUS_READING;
c5:
conn_statuses[conn_indexes[MAX_THREADS-11]]=CONN_STATUS_READING;
c4:
conn_statuses[conn_indexes[MAX_THREADS-12]]=CONN_STATUS_READING;
c3:
conn_statuses[conn_indexes[MAX_THREADS-13]]=CONN_STATUS_READING;
c2:
conn_statuses[conn_indexes[MAX_THREADS-14]]=CONN_STATUS_READING;
c1:
conn_statuses[conn_indexes[MAX_THREADS-15]]=CONN_STATUS_READING;
c0:
conn_statuses[conn_indexes[MAX_THREADS-16]]=CONN_STATUS_READING;
}
This is a daemon that does parallel processing of MAX_THREADS number of connections. As you can see, I have to unroll the loops. For example, it would be nice to have a syntax like this in a compiler:
LOOP(ITERATOR=1,ITERATOR<MAX_THREADS) {
c{ITERATOR}:
conn_statuses[conn_indexes[MAX_THREADS- {ITERATOR}]]=CONN_STATUS_READING;
}
so it would unroll the loop MAX_THREADS number of times and then compile. the c{ITERATOR} is a label to jump to it when the number of threads is lower than MAX_THREADS. But such syntax is difficult to emulate with gcc and even with m4. CUDA has made it defining a kernel in a function, I can do this using inline function, but there is no easy solution to iterate lines like 1,2,3,4 … N and replace the ITERATOR variable. This is kind of tools I am trying to find, but didn’t found yet.
do you really need that performance? may be simple loop will be enough?
Yes Bulat, I really need it to run fast. 16 threads is set for debugging, I will be compiling with MAX_THREADS=256 and higher values.
if you have a server that should serve thousands of client connections simultaneously, it’s a famous C10K problem. just google it to get lots of answers. solutions mentioned in this thread are useless for it
Yes, know about the c10K, I have read about it, that was about 5 or 6 years ago. But today we are working with 1M connections and above. We are using Data Plane Development Kit (dpdk.org) and custom TCP/IP networking stacks … but a lot of code is developed with sequential mentality, and I am changing it into parallel.