I'm ok with this.
On Wed, Jun 05, 2013 at 02:12:36PM -0400, Ted Unangst wrote:
> On Wed, Jun 05, 2013 at 14:13, Alexandre Ratchov wrote:
> > On Tue, Jun 04, 2013 at 11:33:12PM -0400, Ted Unangst wrote:
> >> Instead of using a fixed size hash table for procs, use an rb tree.
> >>
> >> Makes thread/process lookup even more web scale.
> >>
> >
> > any measurement?
>
> o ye of little faith...
>
> stock
> 54.65
> 57.29
> 54.54
>
> rbproc
> 47.27
> 47.34
> 47.16
>
> Benchmark code is below. Now you may well complain that I cooked the
> test to give me the result I want. If you remove the pid colliding
> code pertaining to 42, the results are different.
>
> stock
> 37.16
> 37.52
> 37.07
>
> rbproc
> 47.20
> 46.84
> 46.51
>
> Perhaps a more realistic test is called for, like building a kernel.
>
> stock
> 1m24.51s real 4m6.24s user 0m43.34s system
> 1m24.12s real 4m7.64s user 0m41.98s system
>
> rbproc
> 1m24.02s real 4m6.90s user 0m43.65s system
> 1m23.88s real 4m6.07s user 0m41.73s system
>
> rbproc wins by a hair, but I am happy to call it a draw.
>
> Conclusion? You'll never notice the difference. Personally I have a
> slight preference for improving worst case behavior. The hash table
> isn't *that* large today, but as we increase maxthreads it will get
> bigger. I prefer dynamic structures to statically sized structures.
>
> #include <errno.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
>
> static __inline uint64_t
> rdtsc(void)
> {
> uint32_t hi, lo;
>
> __asm __volatile("rdtsc" : "=d" (hi), "=a" (lo));
> return (((uint64_t)hi << 32) | (uint64_t) lo);
> }
>
> const int loops = 2560000;
> const int maxproc = 50;
>
> int
> main()
> {
> int pidhash = 511;
> int nprocs;
> int pids[200];
> int i, p, pid;
> uint64_t before, after;
>
> printf("creating pids\n");
> nprocs = 0;
> while (nprocs < maxproc) {
> pid = fork();
> switch (pid) {
> case 0:
> if ((getpid() & pidhash) != 42)
> _exit(0);
> while (1)
> sleep(1);
> break;
> case -1:
> for (p = 0; p < nprocs; p++)
> kill(pids[p], 9);
> printf("failed after %d %d\n", nprocs, errno);
> exit(1);
> default:
> if ((pid & pidhash) == 42)
> pids[nprocs++] = pid;
> else
> waitpid(pid, NULL, 0);
> }
> }
> printf("benchmarking...\n");
> before = rdtsc();
> for (i = 0; i < loops; i++)
> for (p = 0; p < nprocs; p++)
> kill(pids[p], 0);
> after = rdtsc();
> for (p = 0; p < nprocs; p++)
> kill(pids[p], 9);
> printf("%.2f\n", (after - before) / 1000000000.0);
> }
>
