Hi, One thing at the onset I would like you to check is that what happens to the program when the loop count is made more like 1000/10,000/100000 - 1 Million/10 Million. Does the Time Graph Increase. Try Plotting the Difference with actual time start. Try Making Use of Some scripting language like TCL/TK. There is some info regarding the select system call. I think it is pertaining to this problem. http://linux.die.net/man/2/syscalls. Basically It is an Optimization that the Current Kernels Look Into. Thanks, Sujit On Sat, Sep 19, 2009 at 1:10 AM, Jürgen Mell <mell@xxxxxxxxxxxxxxxxxxx> wrote: > Meanwhile I have dug a little deeper into this problem. The problem > occurs under the following conditions: > - the BIOS clock must be slow > - the NTP daemon is used to adjust the system time > The problem can be reproduced on real hardware as well as on a virtual > machine running under VMware. Set the BIOS clock back about ten minutes > against the 'real' time. Then start the NTP daemon and then run the > little test program: > > #include <stdio.h> > #include <stdlib.h> > #include <time.h> > #include <errno.h> > #include <sys/select.h> > > int main(int argc, char *argv[]) > { > time_t t; > struct timeval timeout; > int i; > int ret; > > t = time (NULL); > printf ("Current time before = %s", ctime (&t)); > > for (i = 0; i < 20; i++) > { > timeout.tv_sec = 1; > timeout.tv_usec = 0; > > if ((ret = select (FD_SETSIZE, NULL, NULL, NULL, &timeout)) < 0) > { > printf ("select returned %d, errno = %d\n", ret, errno); > return EXIT_FAILURE; > } > } > t = time (NULL); > printf ("Current time after = %s", ctime (&t)); > return EXIT_SUCCESS; > } > > On a virtual machine under VMware I got the following result after some > minutes of system run time: > > hws@cwc-vmware:/home/hws > /space/software/select_test/debug/src/select_test > Current time before = Fri Sep 18 20:05:51 2009 > Current time after = Fri Sep 18 20:06:11 2009 > hws@cwc-vmware:/home/hws > /space/software/select_test/debug/src/select_test > Current time before = Fri Sep 18 20:14:29 2009 > Current time after = Fri Sep 18 20:14:33 2009 > hws@cwc-vmware:/home/hws > /space/software/select_test/debug/src/select_test > Current time before = Fri Sep 18 20:14:57 2009 > Current time after = Fri Sep 18 20:14:57 2009 > hws@cwc-vmware:/home/hws > /space/software/select_test/debug/src/select_test > Current time before = Fri Sep 18 20:15:20 2009 > Current time after = Fri Sep 18 20:15:40 2009 > hws@cwc-vmware:/home/hws > > > Normally, the time distance between 'before' and 'after' should be 20 > seconds as in the first and last run of the program. For the second run > the time difference is only 4 seconds and for the third run it is even zero. > > On the real hardware I have also some other time-related issues when the > problem occurs. Keyboard input will often 'bounce' - key presses are > detected two or more times and some delay times are prolonged (!). I > could not yet reproduce this in the virtual machine. > > The problem will not always occur immediately after the system is > started but it may take several minutes until the first effects occur. I > have not tested this issue with other kernels yet but I will do so > during the weekend. > > Are there any ideas what to do about this (beside buying a better BIOS > clock)? I would really like to have the NTP daemon running to keep the > system time accurate, but somehow it seems to effect wait queues in the > kernel pretty badly. > > Bye, > Jürgen > > Jürgen Mell schrieb: >> Hi, >> >> I have an application which connects via a network socket to a server >> running on the same machine (IP 127.0.0.1) This application uses the >> function 'select' to wait for new data from the server or until a two >> seconds timeout. This works well until there is network traffic on the >> external network interfaces (eth* or WLAN). When there is network >> traffic on the external interfaces, the select function does not wait >> anymore but it returns with a return code of zero, indicating not data >> available on the socket. This happens nearly immediately (after 8 to 9 >> microseconds) and not after the specified two seconds interval. The >> timeout parameter of select is updated accordingly (it shows eg. 1 s >> 999991 us). >> Up to now I could not test this with another kernel but I will try to >> do it this afternoon. Are there any known problems with select? Is >> there any way to circumvent this? >> >> Any help would be greatly appreciated! >> >> Jürgen >> > > -- > Jürgen Mell (Software-Entwicklung) mell@xxxxxxxxxxxxxxxxxxx > Tel.: +49-511-762-18226 http://www.hedrich-winding.com > FAX : +49-511-762-18225 > Mobil: +49-160-7428156 > ---------------------------------------------------------------------------- > HEDRICH winding systems GmbH > An der Universität 2 (im PZH) > D-30823 Garbsen (GERMANY) > ---------------------------------------------------------------------------- > Geschäftsführer: Karsten Adam > Handelsregister: Wetzlar, HRB 4768 > Steuernr.: 020/235/20110 USt-IdNr.: DE 258258279 > ---------------------------------------------------------------------------- > > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- -- Sujit K M blog(http://kmsujit.blogspot.com/) -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
