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SubjectRe: #define HZ 1024 -- negative effects
Well, for kicks, I tried setting HZ to 1024 with 2.2.19. It seemed a 
little more responsive, but that could be psychosomatic. :) I did notice
that I was unable to sync my palm pilot until I set it back to 100.
YMMV. The most useful "performace" tweak for a GUI that I've come across is:

#define _SHM_ID_BITS 10

... if y ou're running Gnome and/or Gtk, because of its appetite for
lots of SHM segments.

-Michael

Mark Hahn wrote:

>>> Are there any negative effects of editing include/asm/param.h to change
>>> HZ from 100 to 1024? Or any other number? This has been suggested as a
>>> way to improve the responsiveness of the GUI on a Linux system. Does it
>>
> ...
>
>> Why not just run the X server at a realtime priority? Then it will get
>> to respond to existing events, such as keyboard and mouse input,
>> promptly without creating lots of superfluous extra clock interrupts.
>> I think you will find this is a better solution.
>
>
> it's surprisingly ineffective; usually, if someone thinks responsiveness
> is bad, there's a problem with the system. for instance, if the system
> is swapping, setting X (and wm, and clients) to RT makes little difference,
> since the kernel is stealing pages from them, regardless of their scheduling
> priority.
>
> if you're curious, you might be interested in two toy programs
> I've attached. one is "setrealtime", which will make a pid RT, or else act
> as a wrapper (ala /bin/time). I have it installed suid root on my system,
> though this is rather dangerous if your have lusers around. the second is a
> simple memory-hog: mmaps a bunch of ram, and keeps it active (printing out a
> handy measure of how long it took to touch its pages...)
>
> regards, mark hahn.
>
>
> ------------------------------------------------------------------------
>
> #include <unistd.h>
> #include <stdlib.h>
> #include <stdio.h>
> #include <sys/time.h>
> #include <sys/mman.h>
>
> volatile unsigned sink;
>
> double second() {
> struct timeval tv;
> gettimeofday(&tv,0);
> return tv.tv_sec + 1e-6 * tv.tv_usec;
> }
>
> int
> main(int argc, char *argv[]) {
> int doWrite = 1;
> unsigned size = 80 * 1024 * 1024;
>
> int letter;
> while ((letter = getopt(argc, argv, "s:wrvh?" )) != -1) {
> switch(letter) {
> case 's': size = atoi(optarg) * 1024 * 1024; break;
> case 'w': doWrite = 1; break;
> default:
> fprintf(stderr,"useup [-s mb][-w]\n");
> exit(1);
> }
> }
> int *base = (int*) mmap(0, size,
> PROT_READ|PROT_WRITE,
> MAP_ANONYMOUS|MAP_PRIVATE, 0, 0);
> if (base == MAP_FAILED) {
> perror("mmap failed");
> exit(1);
> }
>
> int *end = base + size/4;
>
> while (1) {
> double start = second();
> if (doWrite)
> for (int *p = base; p < end; p += 1024)
> *p = 0;
> else {
> unsigned sum = 0;
> for (int *p = base; p < end; p += 1024)
> sum += *p;
> sink = sum;
> }
> printf("%f\n",1000*(second() - start));
> }
> }
>
>
> ------------------------------------------------------------------------
>
> #include <unistd.h>
> #include <stdlib.h>
> #include <stdio.h>
> #include <sched.h>
>
> int
> main(int argc, char *argv[]) {
> int uid = getuid();
> int pid = atoi(argv[1]);
> int sched_fifo_min, sched_fifo_max;
> static struct sched_param sched_parms;
>
> if (!pid)
> pid = getpid();
>
> sched_fifo_min = sched_get_priority_min(SCHED_FIFO);
> sched_fifo_max = sched_get_priority_max(SCHED_FIFO);
> sched_parms.sched_priority = sched_fifo_min + 1;
>
> if (sched_setscheduler(pid, SCHED_FIFO, &sched_parms) == -1)
> perror("cannot set realtime scheduling policy");
>
> if (uid)
> setuid(uid);
>
> if (pid == getpid())
> execvp(argv[1],&argv[1]);
> return 0;
> }
> useup.c
>
> Content-Description:
>
> useup.c
> Content-Type:
>
> TEXT/PLAIN
> Content-Encoding:
>
> BASE64
>
>
> ------------------------------------------------------------------------
> setrealtime.c
>
> Content-Description:
>
> setrealtime.c
> Content-Type:
>
> TEXT/PLAIN
> Content-Encoding:
>
> BASE64
>
>


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