Jan Blunck <jblunck@xxxxxxxxxx> writes: > On Wed, Sep 08, Peter Zijlstra wrote: > >> On Wed, 2010-09-08 at 14:29 +0200, Jan Blunck wrote: >> > This patch is disabling the scheduler tick to go off when there is a task >> > with SCHED_FIFO policy running. Since these tasks are not timesliced anyway >> > we only care about timers, softirqs and such stuff just like when we disable >> > the tick during idle periods. >> > >> >> Also, doesn't this break any and all jiffies users? >> > > Sure. It was enough to make FTQ run. > >> And you need to restart the tick on call_rcu() and everything else that >> requires the tick for processing. >> > > I realized that before as well but somehow forgot about it. Checking for a > disabled timer tick on syscall entry would help. Like we do on irq entry as > well. That doesn't help the gettimeofday/clock_gettime vDSOs which access jiffie like state in user space. I guess you could force the vdso to call into the kernel during such a region, but you cannot force it for an process that is already context switched in this path when the option is first enabled. I guess it would work if you force all the vDSOs to always do a system call at boot, but that's pretty costly. -Andi -- ak@xxxxxxxxxxxxxxx -- Speaking for myself only. -- 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
