Ingo Molnar wrote:
* Lee Revell <[email protected]> wrote:
Well, it is not really a DoS. The rescheduling of the process is
limited by the scheduler and the available CPU time (depending on
the number of runnable tasks in the system).
Shouldn't an unprivileged process be rate limited somehow to avoid
flooding the machine with interrupts? We restrict nonroot users from
setting the RTC interrupt rate higher than 64Hz for a similar reason
(granted, this limit dates back to the 486 days and should probably be
increased to 1024 Hz).
No. An interrupt in this case is really just 'CPU time used up', and an
unprivileged process can take up as much CPU time as the scheduler
allows. So it's _not_ a DoS, and neither is any other unprivileged
infinit loop (or high-rate context-switching task) a DoS.
Ok, may be DOS was not the correct term, but with the 2.6.21 hrt there
is a great difference between an infinite loop and the high-rate
context-switching task (you can try attached programs).
With the first I the system is still responsive, with the latter it
isn't (new process take lot's of time to get created, other process are
very slow).
If it is "just 'CPU time used up'", why I see a such difference between
the 2 cases ?
Maybe the current scheduler failed to handle correctly this case ?
Matthieu
#include <string.h>
#include <sys/time.h>
#include <time.h>
int main()
{
struct timeval tv;
while (1)
gettimeofday(&tv, NULL);
}
int main()
{
while (1)
usleep(1);
}
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